>>10
Sure, there is no way to handle all possible cases. Transformations like rotation are pretty impossible to handle in real time nowadays. But don't even hope to do that. What I am aiming at is unchanged images and images with slight transformations. And with slight transformations I will mainly aim at image resizing and saving in another file format. I don't hope much for transformations like sub images and crops. Still I will give even them a try because it's fun for me.
Most of the people look at the problem from a "do it all" perspective. And of course they find it impossible to do. I am looking at the problem from a "do it fast what you can" perspective. As I don't know any precedents, I don't know whether I will stop at being able to find only unchanged images or more can be done really fast. Either case, the result will be useful at least for me. And as I said: it's fun.
I have also considered the imgSeek's similarity to what I'm willing to make. That project is aimed from the very begining from picture finding from a rough sketch. Contrarary I will aim at pictures very similar to the target. Therefore even if their project went down this is not a downer for me. Because I will take a different path.
Well, you can still be sceptical about this, but I don't think I have much to add. There are two kind of people who hear about my problem: "go for it!" and "give it up!". Choose your side! :)