I've just discovered this article, which talks about comparing two images in Ruby and highlighting the differences.
But if I have images with multiple differences, e.g.: one difference is in the header and the other in the footer it will draw a rectangle on whole image.
Is it possible to draw a separate rectangle on each and every difference?
Not sure about this chunky thing, but if you are looking for multiple image comparison with proper reporting of differences, you should look at a tool called Wraith which is also written in Ruby and is very very powerful for image comparison...
It is created by BBC_News and is open source.
https://github.com/BBC-News/wraith