Best way to compare two images


I’ve started to learn OpenCV. I know that it’s huge library and I have to spend a lot of time to learn it. Because of the library size, and my first steps I’m lost in features…

I want to create tool to get a few information from image. I want to make photos of special display (for example 7 segment display). Then I want to compare these photos with ideal map of icons (in our example - with segments) prepared in eg. Inkscape. In the result I want to get information which segment is lighted up.

I want to use this tool to any other displays - not only 7 segment.

What is the best way to do it?
Thank You in advance for Your support.