Image Discrimina​tion/Compa​rison

I noticed that lots of people have asked about this subject but can't find the discussion that answers it.

Here is the detailed scenario for my question.

I've an standard image of a Keyboard which is projected on a flat table. Now I'm taking a video of the keyboard from which I'm extracting images. Now I've to compare these pictures to standard picture to sense that if any dis-figuration is present or not due to the key-press on the projected image.

It is because that if I don't put any finger on any key of projected keyboard, there is no key press and hence no dis-configuration in standard image; but if there is a key press then there will be dis-configuration in the image.

I want to detect the exact key press location on the standard image to sense which key is being pressed, using matlab.

I hope that I've made my question clear. Thank you for reading and/or attempting to solve it.