Compare a drawing to letters

I'm allowing a user to draw on a canvas. Once tapped OK, I want to compare the drawing with one or more letters (could be double byte). How do I best map the drawing to the letter sequence? 开发者_如何学CI need an approach for scaling, comparing and visualizing. For the later I though to use a 3 color approach: mapping pixels black, letter only pixels green, drawing only pixels red. Would that work?

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Seems like you're looking for OCR. Check out this question for some prebuilt solutions.

OR! Maybe you'd like to use the built-in gesture recognition API to guess those letters instead of rolling your own implementation.