Theory from Practice: Stories and Takeaways from Hacker Camps

Theory from Practice

Stories and Takeaways
from Hacker Camps
October 7th, 2010—Kurateret Torsdag 5, Copenhagen, Denmark
Mark Wubben

A talk based on my experiences at the Mediamatic Social RFID Hackers Camp at the PICNIC
conference in Amsterdam in 2007, 2008 & 2009.

Photo by Marieke Bijster, used with permission. http://www.mediamatic.net/page/105663/
en

I’d like to start this talk by addressing a preconception you may have. A preconception that
says that hackers are those guys who break into other people’s computers. I call myself a
web hacker, but I don’t break into anything. I simply (try to) build cool shit. The hackers and
hacking I’ll talk about are just the same: trying to build cool shit.

Photo by James Kim, http://www.ﬂickr.com/photos/underbiteman/2638246638/. CC-
BY-2.0.

“What hackers and painters have in
common is that they're both makers.
Along with composers, architects, and
writers, what hackers and painters are
trying to do is make good things.”

Paul Graham,
Hackers and Painters

There’s an essay from 2003 by Paul Graham that really shaped my thinking on this. You
should read it: <http://www.paulgraham.com/hp.html>.

So! What do hackers at hacker camps do? They build mobile massage couches!

Photo by Daria Perevezentsev, http://www.mediamatic.net/page/54511/en. Licensed under
Creative Commons, but it’s not clear which speciﬁc license.

Or fun Google battles.

Photo by Mathias Forbach, http://www.mediamatic.net/page/54630/en. Agreement for use
in this presentation with Creative Commons Attribution-ShareAlike license granted via e-
mail.

Or, more realistically, spend time in rooms like these to brainstorm and discuss and to build
their projects.

This was our “shed” for the 2009 Hacker Camp, on a Saturday morning brainstorming
session. The Hacker Camp was organized by Mediamatic and started five days prior to the
PICNIC conference in Amsterdam.

The concept is rather straight forward. Take 20 or so* designers and programmers, add a
bunch of support people, give them five days and material + budget, and see what happens.
This year we produced 8 interactive installations.

* A few people left early on, final projects were done by 17 people

en

A key part of the interactive installations is the so-called “ikTag”. These are produced by
Mediamatic and are RFID tags which can be linked to the social networks that run on the
Mediamatic software. Up to this year the PICNIC network ran on this software and as such we
could use the ikTag to link people to their online proﬁles.

The network provides an API we can use to ﬁnd out who people are, or add new objects to
the website, connect people as friends, etc.

en

RFID
a primer

At this point it’s probably good to discuss RFID a bit. Primarily an RFID chip is a tiny radio
that can send a signal over a few centimeters. There are active and passive RFID chips; active
chips carry a battery and are therefore self-powered, passive chips are powered when they’re
in a magnetic field. RFID readers create this magnetic field, and can therefore read RFID chips
within their range.

RFID chips usually transmit an identifier code, but some can also contain data. RFID chips
used in public transport systems use this capability.

For our installations, we merely relied on the identifier code, which was linked to the
participant on the social network.

Photo by myuibe, http://flickr.com/photos/myuibe/2439798709/. CC-BY 2.0.

This is a Rube Goldberg-like installation from Jack Schulze of BERG London and Timo Arnall
of the Touch research project. It shows RFID tags affecting RFID readers, which cause an
action that causes another RFID tag to affect another reader, and so forth.

Video embedded from http://vimeo.com/6588461.

As I mentioned, the RFID tags and readers have only a limited range. Now, strictly speaking
you can build readers that can read tags from several meters away, but that’s usually not
within the scope of interactive installations.

This video shows a visualization of the range of tags and readers, and was again created by
BERG London and the Touch project.

Video embedded from http://vimeo.com/7022707.

Some Projects
from the past few years

Let’s look at some projects that were created at Hacker Camps in the past few years. Some of
these we’ll return to later during this talk.

en

Photo Booth ’07
Photo Booth was a social photo booth. You could sit inside it with friends and use your RFID
tag to identify yourself, then the camera would take a picture with you and your friends and
put it on the social network.

A screen outside of the booth allowed you to call up the photos taken with you in them.

Made by Timo Arnall, Einer Sneve Martinussen, Jørn Knutsen & Anne Helmond. Find out more
at http://www.mediamatic.net/page/22730/en.

Photo by Anne Helmond, CC-BY-NC-SA 2.0. http://www.ﬂickr.com/photos/silvertje/
1441886446/

It was run by two laptops, two RFID readers, a webcam, and two displays. Oh, and a lot of
wood.

1446632325/

Screenshot from http://www.mediamatic.net/page/29317/en.

Mobile Massage Couch ’08
If you’re tired after a day of conferencing the Mobile Massage Couch would come in handy.
It’s battery powered, has wheels, and gives free massages. Both armrests have an RFID
reader, on which you put your RFID tag to receive a massage. Other people can place their
tag on the armrest to recharge your massage credit. And, for even more social interaction, if
you use the couch with somebody else, you’re automatically connected on the online PICNIC
network.

Made by Edwin Dertien, Fabienne Serriere & Ralph Meijer. Find out more at http://
www.mediamatic.net/page/52720/en.


ikWin ’08
Google popularity contest! RFID tags are used to find your profile name, then a Google search
is performed. The person with the highest number of search results, goes highest.

This was created at last years PICNIC, and very cleverly uses non-modified stage elevators to
do the heavy lifting. Custom mechanics are used to press the up and down button.

Made by Axel Roest, Mathias Forbach & Simon Claessen. Find out more at http://
www.mediamatic.net/page/52953/en.

Photo by Mathias Forbach, http://www.mediamatic.net/page/54630/en. Agreement for use
in this presentation with Creative Commons Attribution-ShareAlike license granted via e-
mail.

ikWin ’09
Axel & Simon, together with Mediamatic, continued development of the ikWin. As you can see
in this photo it has a proper construction that is easily moved. They’ve also improved the
mechanics for pushing the elevator buttons, as well as a better “altitude” meter.

Vbird ’08
Small disclaimer, I worked on this project. And it failed, quite miserably. But, the concept was
to have a flightless bird that you had to throw to other people so it could fly. It would record
its flights. Combined with a wireless RFID reader in the bird, it could identify you and upload
a video to your online profile. There also were sound effects when it had read your RFID tag
or when you threw it into the air.

Sadly the hardware was in a very cramped space where it was hard to maintain. And, you
know, we were throwing with it. We used it for a bit at the end of the first day, but after that
it kept breaking and breaking.

Made by Adriaan Wormgoor, Eelco Wagenaar, Erik Borra, Mark Wubben & Martijn Pannevis.
Find out more at http://www.mediamatic.net/page/52865/en.


Videos from http://www.justlol.net/vbird/.

Breaking the Frame ’09
A clever setup takes several pictures at once from different angles, which are then put into an
animated sequence. Do something crazy and see how it turns out! Of course the animations
are uploaded to your PICNIC proﬁle.

Made by Carl Emil Carlsen, Dan Paluska & Mike Wege.

en

Sequence from http://www.mediamatic.net/page/111800.

Cool, huh?

This would be a good time to ask the audience what they thought of these projects, what was
good, what was bad, why do they think that is?

Takeaways
six of ‘em!

Now let’s look at six things I learned from doing these Hacker Camps. They’re not really
lessons or rules, and they’re quite connected to each other. Don’t get too hung up on what I
call them.

Photo by ginnerobot, http://ﬂickr.com/photos/ginnerobot/2877212845/. CC-BY-SA 2.0.

Simplify, simplify, simplify
simplify even further

1
Simplify, simplify, simplify. I can’t repeat this enough, because it’s an incredibly useful
mantra when doing these kind of projects. The challenge of a Hacker Camp is to create
something fun and meaningful in very little time, with a rather hard deadline. You don’t want
PICNIC to start while your still working on your project, and you definitely want people to
interact with your installation!

The only way to do this is to radically simplify your idea. And then again. And again. And,
well, you get the point. Quite often when you first conceive of something you tend to
overcomplicate. If you’re a programmer you’ll love collecting data and statistics, if you’re a
designer you love building pretty interfaces. Quite often these things don’t matter at all.

Especially at conferences like PICNIC where the participant has only a very short attention
span, since they’ll find your installation on their way to something else. You’ll have to grab
their attention, get them to interact, give them a valuable moment and let them move on.

Vbird ’08
The reason Vbird failed was that we tried to cram too much technology into it. What came up
in the brainstorming was that we wanted to make a game about throwing things. Someone
mentioned a project done at the Lowlands festival earlier that year called the Jubilator, where
they had a huge ball with a camera and a microphone in it that was being thrown around in
the crowd.


Here’s some video footage from the Jubilator. As you can see, people at the festival had great
fun with it, but we had to add some RFID to it as well.

So, we made a bird that contained an RFID reader. And then it wasn’t too much of a stretch to
add an accelerometer as well. And then we made it track who you threw it to, and made it
make sounds when it was flying, and uploaded video to your profile.

The end result? A hugely complicated object that kept breaking. And, of course nobody cares
about the camera and having the video on their profile. They want to throw things! Nobody
cares about the cool Flash interface we built so bystanders could see what was happening. It
was all too much!

Video embedded from http://www.youtube.com/watch?v=0PbZNSpHMZM. More about
Jubilator at http://www.jubilator.org.

ikSpin ’09
A week or so before last year’s PICNIC I started thinking about project ideas. I realized that
the real fun of playing with the Vbird was throwing it to other people. The largest problem
was that we were throwing the hardware. So I figured, let’s flip the concept and throw with
RFID tags instead! At least those won’t break…

Throwing RFID tags meant I had to come up with a game where you could throw the tags and
“touch” down on an RFID reader. But, it also restricted the possible throwing objects. In most
games you throw with either balls, frisbees or boomerangs. As we’ve seen earlier RFID has
some constraints as to from which angles it can be read out. Because of this, a flat object is
the easiest to stick some RFID tags on so they can be read reliably. Hence we arrived at
frisbees — boomerang seemed a bit too tricky.

With this in mind I arrived in Amsterdam, where the concept would simplify even further.

en

Eelco Wagenaar
This, by the way, is Eelco, with whom I’ve built the ikSpin project. Eelco was also part of the
Vbird team, in fact, he’s the guy who made the bird.

en

As discussed, the RFID-equipped RFID tags had to touch down on a reader as part of the
gameplay. The initial concept I had was to have two teams with different colors. There’d be a
number of bases – to touch down on – that could send out light signals in the team colors. As
your team, you’d have to look for the base that was sending out your light signal and get
your frisbee there on time to make a point.

So what’s going on in this scenario?

* Two teams that have colors
* A number of bases that can send out two different colors
* Two teams looking at all of the bases and then heading to different ones
* You’d make a point by getting to your base before the other team got to theirs
* Fun clashes when both teams need to get to the same base

If this sounds complicated, you’re right. After feedback from Willem Velthoven, director of
Mediamatic and mentor of the teams, we arrived at the following concept:

* Two teams
* One base emits both a light and sound signal
* Both teams need to score at that one base
* We’d measure the time it took for each team to score their points
* Fastest team to get to X points would win

This is what we started to write the software for, but it was still too complicated. If the first
team scored, why would the other team still try to make it to that base? And why is it
important who had the fastest scoring times? Why not let the first team to score X points win?

However, we kept the concept of total time to score your X points. Fastest team of the day
would get a special mention on their profile page. As it turned out, this code didn’t work for
some reason, and I never fixed it because let’s face it, nobody cares about being the fastest
team. The gameplay itself is way, way more important and way more fun than some silly
statistic.

en

Badger ’07
It’s funny, actually, to compare the Vbird and subsequent ikSpin to an installation I built in
2007 (with Jim Wood & Audrey Samson). It was an installation called Badger that consisted of
nothing more than an RFID reader, a speaker and a printer. You could scan your RFID tag, the
speaker would announce “Thank you, now printing” and the printer would print a sticker
sheet with a cute animal icon. Which icon you would get was determined by looking at your
PICNIC proﬁle.

Find out more about Badger at http://www.mediamatic.net/page/22590/en.

Photo by Marieke Bijster, used with permission, CC-BY-NC 2.0. http://www.mediamatic.net/
page/74925/en

Some of the icons one could get. I spent quite some time on mapping proﬁles to one of
twelve categories, which in the end didn’t work very reliably at all. Thing is, the point of the
installation was to lower the barrier for interaction — seeing somebody with the same badge
would give you an excuse to talk to them. For the people standing in line, the fun was in
seeing what would come out of the printer and then getting a button and a sticker. A payoff,
something personal.

Yes, there needed to be an *illusion* that the icon was based on you as a person, but really?
It should have been a random distribution, nobody would have noticed.

Photo by Marieke Bijster, used with permission. http://www.mediamatic.net/page/23362/en

When building interactive installations, it’s about the real value of the experience. Hopefully
this video of French students playing with the ikSpin is a good illustration of that.

Something not captured on video are the two rules of playing ikSpin:

1) No running, your teammate needs to be near the base to catch your frisbee and make the
point.
2) No falling. We added this rule after the ﬁrst day, where an overly enthusiastic player fell
and broke her elbow. She also turned out to be the director of the museum of modern arts
in Lima, Peru…

---
To point out in replay:

* 00:20 Registration interface
* 00:50 Blinking light at top of base
* 00:54 Scoring announcement, recorded at 2 AM in a small meadow about 150m from the
square.
* 01:08 Notice how the point is made with the frisbee’s surface facing down. This causes the
RFID tags to be closer to the reader, improving your chances of the frisbee being
recognized and you scoring the point. Notice how this related to the readable area as
shown by BERG London & Touch?
* 01:14 Again the frisbee is placed face down to make the point. I might have told them this
was the best way to do, but perhaps they just picked it up by themselves. (This is not the
ﬁrst game they played.)
* 01:18 Another very nice shot of a face down frisbee, this time the white one. You can see
the RFID tags, too.
* 01:48 Announcement that Team Orange is now at game point
* 01:54 Team Orange wins! No displays, just a speaker announcement. Not always noticed by

Constraints are freeing

2
Not only do you need to focus on simplifying your concept, you are also constrained in
*what* you can make. Yes, Mediamatic had a budget for the Hacker Camp, and it was quite a
large budget, but it’s not inﬁnite. Lower cost is probably better. There’s also the problem of
having to ﬁt in with the rest of the conference, is there enough space for your installation?
We’d have loved to have a somewhat bigger space to play ikSpin in. Another problem could
be whether your installation is supposed to be used inside or outside, and how does that
affect how you construct it?

But perhaps the biggest constraint is that of team size, and usually not because you have too
few people, but because you have too many. If you have a large team you think you can build
what ever you come up with after the first round of simplification, and you never simplify
further.

With Vbird, we had work for 4.5 people, and there were five of us. Which meant that we could
build the camera, the wireless RFID reader, the wireless accelerometer, the encoding of the
video, the uploading to the PICNIC site, the visualizations, the bird, etc. But as we just saw,
that was all completely irrelevant to what really mattered: throwing things to other people!
The lack of constraint in the personnel department meant that we didn’t simplify enough.

In fact, this year a rule was set that the larger your team, the less help you would get from
Mediamatic staff.


ikSpin Construction

Let’s have a look at how constraints affected the construction of ikSpin.

en

Here’s the original sketch again that Eelco made. The colors are irrelevant, but what’s
interesting is the shape we both had in mind for the bases and the registration tower.

Somehow these shapes are the ﬁrst thing you think of. Wooden, pyramid-like structures.
There’s room for a light under the top, and the RFID reader is embedded within the top.
Inside we can then hide an Eee PC which we would use to run the system. We’d have a power
cable and a network cable coming out of the structure, and a hatch to do maintenance.

In fact, that Eee PC there is already a change of my original idea. The optimal base would be
completely wireless, so it would have to run on batteries and communicate wirelessly. Since
we couldn’t set up our own WiFi network at PICNIC, and since the existing network would be
way too slow for our purposes, this would have to be build using Arduino hardware and an
XBee radio controller. I have zero experience programming this, and neither did Eelco.
Therefore we decided to use Eee PC’s instead, on which I could write Python code. Much
better!

We discussed the previous sketch with Willem, who asked if there wasn’t something that
already existed that we could simply reuse. A good point, because building several wooden
bases is a lot of work! We couldn’t quite think of anything, safe for a garbage container.
Which wouldn’t have been the best idea…

So Eelco went to the nearby hardware store looking for inspiration, and found these buckets
used for mixing mortar. Creative stacking lead to many possibilities, so we decided to pursue
this further.

Photos by Eelco Wagenaar, used with permission. http://www.flickr.com/photos/_wgnr/
4089406426/, http://www.flickr.com/photos/_wgnr/4089406586/, http://www.flickr.com/
photos/_wgnr/4089406740/.

A ﬁrst sketch using the mortar buckets.

A more complicated sketch where we tried to ﬁgure out construction and where to ﬁt the
various components.

Another sketch of the top part.

When actually setting up this structure though it became apparent that it was far too high.
Not that I personally had much trouble with it, but then again I’m a tall Dutchman.

In the end this is the design we settled with. Two black buckets on top of each other, with
50kg of counterweight sand in the bottom one. The hardware was subsequently taped to the
top of the upper black bucket, with velcro for the laptops so we could remove them at night.
The genius of this setup is that we could simply lift the white bucket to do maintenance, and
the structure was water-proof to boot!

You may also notice that the pole for the light is now placed in the center. The RFID reader is
placed at the “bottom” of the white bucket, so at the surface of the base.

Something you can’t see from this photo is that this was actually our ﬁrst working setup, with
three laptops in the three bases and the laptop on the right running as the coordinating
server.

Here’s a photo of Eelco ﬁtting a wooden plateau inside the bottom bucket for the pole to rest
on.

And this is us walking back from the hardware store with the material for the ﬁrst few bases.

Have a Plan B

3
Even with these constraints and after countless simpliﬁcations, you should always have a Plan
B in case things don’t work out.

With Vbird, we had no Plan B. Sure we had backup hardware, but we couldn’t signiﬁcantly
change anything to make sure it stopped breaking.


For ikSpin we were quite certain early on that it was doable and would work. The design of
the bases allowed us to swap out parts if needed, and indeed we did replace the RFID readers
of a few bases. We also had four bases, where we needed a minimum of three for decent
gameplay, and two for at least some gameplay. Had one base failed, we’d have had three left.
Had another one failed we’d still have two bases, and with a few changes to the software
could have made a game even out of that.

Photo by Eelco Wagenaar, used with permission. http://www.ﬂickr.com/photos/_wgnr/
3986886013/.

Breaking the Frame ’09
The Breaking the Frame team initially wanted to use proper cameras to take the photos. This
is the picture of the moment where they have to make the decision to go to Plan B and use
webcams, because they can’t get the normal cameras working.

Sadly they only had Mike (on the right) who could work on using the proper cameras, so Carl
Emil (on the left) and Dan (not in picture) had very little to do initially. With hindsight, they
probably should have started with the webcams and tried to hook up more of them and
improve the interaction.

en

DuckRace ’08
DuckRace was a project inspired by Mario Kart. Wiimotes were used to send control signals to
a computer, which then translated those signals into the controls for the cars. Two players
would race across the track to the other side (there’s a corner just outside of the picture
around the middle barrier). Observers could root for one player and negatively affect the
ability of the other player to control is car.

The team had much difficulty in moving from prototype on their own laptops to the setup in
the main area with the Mediamatic laptops. I believe the project was up at the end of the
second day, and only then with just the controls, no possible actions by the audience. And
controlling the cars was quite hard even without those.

In the end, the “Plan B” consisted of not implementing features. That, sadly, is not a Plan B.

Made by Dirk van Oosterbosch, Heerko van der Kooij, Marc Boon & Vlad Trifa. Find out more
at http://www.mediamatic.net/page/52665/en.

Photo by Daria Perevezentsev. http://www.mediamatic.net/page/54939/en

Now, I’m not here to dump on other teams or people, but it *is* important to set out
achievable milestones for your project. These should be planned in such a way that you can
*know* whether you’re going to make it, and to have clear fallbacks in case something does
not work.

Of course this isn’t going to be very formal, but it’s worth it to be thinking about this.

In this picture, taken on the second day of the camp, I’m already setting up the laptops we’re
going to use. I’m also writing code on my own machine. When I left for bed that night the
laptops were already talking to each other. By Sunday afternoon we had our ﬁrst test setup. I
didn’t write down a formal plan for this, but did plan mentally to have the software in a
working state by the end of Sunday, so we could start testing it and using it on Monday.

The point of having a Plan
B is to never need it.

The point really of having a Plan B is to never need it in the ﬁrst place. Thinking about a Plan
B forces you to be realistic about Plan A, and hopefully scale it down to the point where it is
achievable. And sure, you can plan for experimentation, but that shouldn’t take more than a
few hours, not days like with Breaking the Frame.

“Share Your Shit”
—Tor Nørretranders

4
“One organism’s shit is another organism’s food.” [^1] You can’t be a hacker without sharing
your work, and you can’t do a Hacker Camp without reusing work by others. Over the years
Mediamatic has evolved a set of tools we could use to build our installations, something that
really paid of this year as the tools matured.

[^1] Stowe Boyd, http://www.stoweboyd.com/message/2008/06/share-your-shit.html
See also http://www.ﬂickr.com/photos/tonz/2614647984/.

Photo Booth ’07
A really awesome example of this is the evolution of the Photo Booth from 2007. This huge
structure, running of two laptops.

1447486358/

See, two laptops!

1441886158/

ikCam ’09
Which by 2009 has turned into an open source program running on an Eee Top with an
integrated webcam to take the picture and the RFID reader for identifying users. I believe a
future version will even be capable of recording video!

It’s amazing to see how this huge Photo Booth has been turned into a piece of software that,
two years later, was used to power *two* projects. ikSpin used a modiﬁed version of the
ikCam to register the teams. Each team would take a picture with their frisbee, the team
photo was proof of them playing, and we would indeed add text to the photo to show
whether the team won or lost, and against whom they played.

Breaking the Frame used a modiﬁed version of the ikCam to take their sequence of pictures
and upload an animated GIF to the PICNIC website.

In fact, all our software and documentation material is open source. See http://
trac.mediamatic.nl/picnic!

en

Here’s a picture of our brainstorming session on the 1st day of the Camp. At this point
everybody was just sharing their ideas, get feedback and come up with more ideas. On the
2nd day people proposed the ideas they wanted to pursue, teams were formed and the rest is
history.

Find a Mentor

5
Earlier in this presentation I’ve alluded to feedback we got from Willem Velthoven. It’s
incredibly valuable to be able to talk to somebody who can provide a new perspective on your
project. Willem pushed us to simplify and it worked out for the better. Finding somebody with
more experience and a different perspective is always a good thing.

Willem Velthoven
en

Get a Support Team

6
When you have ﬁve days… you don’t want to worry about ﬁnding blinking lights in a strange
city. You don’t want to spend three days building your structure on your own. You don’t want
to worry about where to get lunch. In other words, you need a support team.

And Mediamatic took care of that brilliantly. From people doing supply runs…

en

…to painting…

en

…and drilling…

en

…and more supply runs…

en

…and technical support…

en

…and creating posters, Mediamatic did it all.

Get outside help so you can focus on what matters most: building awesome projects.

Important about these kind of installations is that you can do it yourself. RFID tags, readers,
electronics, it’s all easily accessible and quite inexpensive. Even though there was a fairly
large budget for the Hacker Camp you can easily do these projects as a hobby. There’s no
need anymore to live in a world that is produced for you, you can put new things that *you*
make into this world.

As Matt Jones would put it, GET EXCITED and MAKE THINGS!

Illustration by Matt Jones, CC-BY-SA-NC, http://www.ﬂickr.com/photos/blackbeltjones/
3365682994/.

Tusind tak!

Mark Wubben

supercollider.dk & novemberborn.net
twitter.com/novemberborn

11born.net/tandp

Licensed under Creative Commons Attribution-Share Alike 2.5
http://creativecommons.org/licenses/by-sa/2.5/dk/

And that concludes this talk. Thank you for your attention.

Special
Thanks

Anne Helmond
Daria Perevezentsev
Eelco Wagenaar
Marieke Bijster
Mathias Forbach

Mediamatic

Special thanks to the following people, who provided material for this talk:

Anne Helmond: http://www.annehelmond.nl
Daria Perevezentsev: http://www.mediamatic.net/person/51156
Eelco Wagenaar: http://www.mediamatic.net/id/22662
Marieke Bijster: http://www.mariekebijster.nl
Mathias Forbach: http://www.ﬁchtre.ch

Mediamatic: http://mediamatic.net

Photo by Lali Masriera, http://ﬂickr.com/photos/visualpanic/183356975/. CC-BY 2.0.

James Kim
myuibe
ginnerobot
Matt Jones
Lali Masriera
Jeff Kubina

Many, many thanks to the wonderful people on Flickr who licensed their photos under
Creative Commons.

Photo by Jeff Kubina, http://ﬂickr.com/photos/kubina/903033693/. CC-BY-SA 2.0.

Theory from Practice: Stories and Takeaways from Hacker Camps

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