How to identify pictures correctly?

Question

Images

The essence of the question.
C# .NET
have a function

Function(Image scr, TesseractEngine engine)
        {
            var cropped = CropImage(scr, new Rectangle(261, 1210, 200, 51));
        }

In it, we crop part of the image - and
then I have such a strong plug.
There are about 20 variations of such images.
I could cut them in advance.
But how can I bring them to a single form - for example, calculate the size in bytes or something else unique - how could one determine that the sliced ​​​​picture is a conditionally 3 picture - does the value mean such and such?
How to be?
PS Pictures differ not only in color but also in symbols on them.

Answer 1

https://ru.wikipedia.org/wiki/%D0%A5%D0%B5%D1%88-%...