multiple choice test mark reader - where to start?

I was assigned a project (in school) for automated multiple choice test scoring and I do not know where to start.
I think his is a kind of popular program and you already know about it. Enter an image file scanned of the answer sheet and return results.
Everything I know about computer vision is a few examples of photo editing with OpenCV. I hope you can give me a few keywords related to the problem or maybe a couple of blog articles, documents and related libraries.
Is there any free open source programs that I can refer to?

Edit: Add 2 example of the answer sheet (sory that I cannot find a sheet in English):

I think there are basically two steps to the problem

1. bring the form into a normalized position
2. now you know where the boxes are and can look at them by thresholding the gray values in that region.

What methods to use for step 1 depends on your actual images and how much the vary. Do you have some example images you can upload?

Also I think it is a good idea, especially if you are a beginner, to start with some simple examples and work your way up from there by adding more and more variation.