The document discusses various topics related to human-computer interaction (HCI) including goals of HCI, limitations on interactive performance, interaction styles, CAPTCHA and its history and working. Some key points: - The principal goal of HCI is to develop usable, safe and efficient systems for end-users by understanding how users interact with systems and designing tools that allow user-centered access and interaction. - Interactive performance can be limited by factors like computation, storage, graphics and network capacity. - Common interaction styles include command lines, menus, natural language, forms/spreadsheets and WIMP (windows, icons, menus, pointers) interfaces. - CAPTCHA is a type of

1. Human Computer
Interaction
HCI

2. Goals of HCI
• The principal objective of HCI is to develop functional systems that are usable,
safe, and efficient for end-users.
• The developer community can achieve this goal by fulfilling the
following criteria:
❑ Have sound knowledge of how users use computing systems.
❑ Design methods, techniques, and tools that allow users to access systems
based on their needs.
❑ Adjust, test, refine, validate, and ensure that users achieve effective
communication or interaction with the systems.
❑ Always give priority to end-users and lay the robust foundation of HCI.

3. Limitations on interactive performance
There are several factors that can limit the speed of an
interactive system:
• Computation bound
• Storage channel bound
• Graphics bound
• Network capacity

4. Interaction Styles
• Interaction can be seen as a dialog between the computer and the user. The
choice of interface style can have a profound effect on the nature of this
dialog.
• 1- Command line interface
It provides a means of expressing instructions to the computer directly,
using function keys, single characters, abbreviations or whole-word
commands. In some systems the command line is the only way of
communicating with the system, especially for remote access using telnet.
• 2- Menus
In a menu-driven interface, the set of options available to the user is
displayed on the screen, and selected using the mouse, or numeric or
alphabetic keys. Since the options are visible they are less demanding of the
user, relying on recognition rather than recall.

5. Interaction Styles
• 3- Natural language
The ambiguity of natural language makes it very difficult for a machine to
understand.
We often rely on the context and our general knowledge to sort out these
ambiguities. This information is difficult to provide to the machine.
It is important in interfaces which use natural language in this restricted form
that the user is aware of the limitations of the system and does not expect too
much understanding.
4.Question/answer and query dialog
Question and answer dialog is a simple mechanism for providing input to an
application in a specific domain. These interfaces are easy to learn and use, but
are limited in functionality and power. As such, they are appropriate for
restricted domains (particularly information systems) and for novice or casual
users.

6. Interaction Styles
• 5.Form-fills and spreadsheets
• The user works through the form, filling in appropriate values. The data are
then entered into the application in the correct place. Most form-filling
interfaces allow easy movement around the form and allow some fields to be
left blank.
• 6.The WIMP interfaces
• WIMP stands for windows, icons, menus and pointers (sometimes windows,
icons, mice and pull-down menus), and is the default interface style for the
majority of interactive computer systems in use today.
• 7.Point-and-click interfaces
• virtually all actions take only a single click of the mouse button. You may point
at a city on a map and when you click a window opens, showing you tourist
information about the city.

7. Interaction Styles
• 8.Three-dimensional interfaces
• The most obvious example is virtual reality, but VR is
only part of a range of 3D techniques available to the
interface designer.
• The simplest technique is where ordinary WIMP
elements, buttons, scroll bars, etc., are given a 3D
appearance using shading, giving the appearance of
being sculpted out of stone.

8. CAPTCHA and Human Interaction
• CAPTCHA, Completely Automated Public Turing Test to tell Computers
and Humans Apart, is widely used as a security mechanism to classify
human and computer.
• This security mechanism is based on the Turing Test, which has been
conceived to ensure network security.
• Usability is another fundamental issue, which can avoid human users
proceeding tedious and time-consuming operation.
• CAPTCHA design should consider security and usability simultaneously.
• CAPTCHA ,also called HIPs (Human Interaction Proofs) , is a test to classify
human users and computer.

10. CAPTCHA and Human Interaction
The idea of CAPTCHA is derived from the Turing test ,however it is different from
Turing test in three folds:
• Firstly, the generating and scoring of CAPTCHAS are finished by machine
automatically;
• Secondly, the purpose of designing CAPTCHA is to identify the difference between
human and computer, instead of avoid distinguishing;
• Thirdly, CAPTCHA is a kind of security mechanism, while most Turing tests are
used as an indicator to reflect the progress of AI. Therefore, CAPTCHA is usually
regarded as a kind of Reverse Turing test for humans and computer classification.

11. CAPTCHA and Human Interaction
Examples:
• CAPTCHA: x9Pm72se
• Input: x9Pm62es
• Output: CAPTCHA Not Matched
• CAPTCHA: cF3yl9T4
• Input: cF3yl9T4
• Output: CAPTCHA Matched

12. CAPTCHA and Human Interaction
• The set of characters to generate CAPTCHA are stored in a
character array chrs[ ] which contains (a-z, A-Z, 0-9), therefore
size of chrs[ ] is 62.
• To generate a unique CAPTCHA every time, a random number is
generated using rand() function which generates a random
number between 0 to 61 saved to the character array chrs[ ]
• This loop runs n (length of CAPTCHA) times to generate
CAPTCHA of given length.

13. History of CAPTCHA
• Around 1997, AltaVista (a primitive search engine of that decade) was having
a tough time fixing the high number of auto URL assets that were hampering
its website ranking process severely.
• To solve this issue, the chief scientist of AltaVista, created an algorithm that
later became famous as CAPTCHA.
• The algorithm was capable of introducing a series of autogenerated and
random images with printed text. The algorithm was based on the hypothesis
that if these surge URLs are created by a bot or computer, CAPTCHA can stop
them from visiting the website as they won’t be able to identify the images.
• In 2016, Jason Polakis, worked on the difficulty level of CAPTCHA and figured
out that the algorithm is so complex that even humans can fail to recognize
the images. That makes it tougher for bots as well as and computers. Hence,
it’s considered a viable tool to control undesirable website access.
•

14. How does CAPTCHA work
• Customers should separate letters in exemplary CAPTCHAs.
• The letters are misshaped with the target that bots are not committed
to have the choice to recollect them.
• clients need to interpret the twisted substance, type the right letters
into a plan field, and present the development.
• Such tests are standard in login structures, account information
exchange structures, online audits, and web business checkout pages.
• The best that different bots will truly have to do is input some irregular
letters, making it really dubious that they will finish the assessment. In
this way, bots bomb the test and are hindered from partner with the
site or application, while people can keep on utilizing it like common.

15. Advantages of CAPTCHA
Using CAPTCHA is preferred because:
• It’s highly worthwhile to discourage spam and unwanted
access.
• It can stop fake and ill-intended website access or usage.
• CAPTCHAs are an easy way to improve the website’s
accessibility.
• For human minds, making sense of CAPTCHA is easy.

16. Disadvantages of CAPTCHA
• Don’t consider CAPTCHA as a foolproof tool as it’s not. It’s most effective for
spam.
• Solving CAPTCHA needs time and effort, which is not feasible for every
website user. Some might even drop the idea of visiting a website if it uses
CAPTCHA. Hence, it might lead to a certain drop in website traffic
• CAPTCHAs are not suitable for visually impaired users. So, you won’t be able
to target such users if you use CAPTCHA.

17. Types of CAPTCHA
a) Text CAPTCHAs
• The most standard kind of check is text CAPTCHAs.
• These characters are shown in an odd style by the CAPTCHA, requiring
translation.
Strategies for making text-based CAPTCHAs include:
• Gimpy
• EZ-Gimpy
• Gimpy-r
• Simard's HIP

18. • Gimpy
• The gimpy selects a handful of emotionally charged words from a
rundown of 850 words and conveys them in an unusual manner.

19. • EZ-Gimpy
• It's an assortment of Gimpy that just utilizes a single word.

20. • Gimpy-r
• This picks reassuring letters, then bends and embellishes them
with foundation discontent.

21. • Simard's HIP
• This method picks alphabets and numerals at random and then
alters them with curves and shadings.

22. b) Image CAPTCHA
• A few photographs of ordinary things are compared. The customer should feature
which photographs have all the earmarks of being the most significant or show which
ones tackle a semantic issue.
• picture-based CAPTCHAs give preferred security over text-based cycles.

23. c) Audio CAPTCHA
• Audio CAPTCHA is a reverse Turing test to discriminate the user as
human or bot using audio as a medium. As W3C guidelines mandate
the need of accessibility of web for people with disabilities like visual
or motor impairment, audio CAPTCHA

24. • D) Math or verbal problems
• CAPTCHAs are also used in the same way as enrollment tries are. They
incorporate exercises errands and general information requests.

25. • reCAPTCHA Definition
reCAPTCHA is a more advanced version of the standard CAPTCHA tests. Some
reCAPTCHAs, like CAPTCHA, require consumers to submit images of text that PCs have
difficulty interpreting. Unlike traditional CAPTCHAs, reCAPTCHA gets its content from real
images: photographs of street addresses, text from printed books, text from historical
newspapers, and so on.

26. CAPTCHA VS.reCAPTCHA
• A CAPTCHA is a test designed to differentiate between real human users and
malicious bots. ReCAPTCHA is a CAPTCHA system developed by Google.
• A CAPTCHA is any website authentication test designed to tell humans and
computers apart. There are several types of CAPTCHAs owned by different
companies/providers. ReCAPTCHA is Google’s popular CAPTCHA service, used
for basic bot protection and other purposes. For example, Google used images
from scanned books to help digitize The New York Times archives and books
from Google Books.
• Advanced bots threaten all websites that rely on traditional CAPTCHAs alone to
keep cybercriminals at bay. Businesses can keep their platforms safe by using
an integrated CAPTCHA built into a sophisticated and personalized bot
protection solution.