Learn how to detect changes in documents and images using free software released by the National Institutes of Health.

1. By Charles Nichols

2. Can you find the differences?

3. How about now?

4. Pretty obvious now, eh?

5. The solution. Did you find them all?
Cheek
Bones
Belt
Ornaments
Sash Color
Sandal
Strap
Pavement
Cracks
Balls
Chimney
Bow
Switched
Sides
Anklet
Sash
Length

6. ImageJ software from the National Institutes of Health, link:
http://rsbweb.nih.gov/ij/download.html
Calculator Plus plug in:
http://rsbweb.nih.gov/ij/plugins/calculator-plus.html
How did I do it? Using free software.

7. Download the image and note its size, 600w 672h.
http://blogs.baruch.cuny.edu/fro12dtg/files/2012/11/Assassins-Creed-
Revelations-game-600x672.jpg
The image is mirrored down the middle, so each image is 600w x 336h. Save
these sections separately and label as Top and Bottom using your favorite
image editor.
Create the Reverse Image by puttingTop on Bottom and Bottom on top.
Open ImageJ software after installing the Calculator Plus plugin.
Step 1: Create a Reverse Image

8. Step 2: Subtract the Images
- =
Original Image Reversed Image Result, after auto contrast
This is referred to as background subtraction.

9. Step 3: Multiply the Result by Itself
x =
Subtracted Image Subtracted Image Result, after saturation

10. Step 4: Overlay images, making white
transparent and washing out the original.
+ =
Washed Out Image Subtracted Image Result, after auto contrast

11. Small details were skipped, but can be figured out pretty quickly.
Here’s another example from a Geocache. Differing numbers indicate coordinates:
That’s It!

12. Solution:
That’s It!
These are misalignment errors.

13. Misalignment errors were caused by one or two pixel offsets in the baseline
image.
Here, a baseline image was given and had to be manually aligned for all ten
digits.
Here’s the baseline.Try it yourself!
Misalignment Errors

14. If you can do it with images, you can do it with a video an in real time!
Check out these videos:
Telecommunications and Imaging Laboratory
Institut Montefiore - University of Liege, Belgium
http://www2.ulg.ac.be/telecom/research/vibe/
Other Uses for this Method

15. DetectingChanges in Documents is Easy