Update (26 Jan, 2014) :
Happy to see so many people taking interest in image processing asking me doubts and clarifying them. So, just want to remind you of the golden problem in image processing. Recognition. You are given only a single photo of a person. Like something captured on a hidden camera. Now you are given a criminal database of photographs, containing the images of ten thousand criminals. Now your recognition engine, should perform search in such a manner, that the first time it says a HIT, the criminal should be the exact one they are looking for. Try to solve this. Write a paper. Take patent. The whole world's police may want to buy it.