Image/Symbol Recognition in iOS using OpenCV

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Hi,

I"ve been trying to use the image recognition features of OpenCV to recognize the main features of a Tic Tac Toe board (i.e. the grid, how many spaces have been filled, how many Xs and Os etc.) but I've been have some trouble coming up with a method to solve this problem.

My plan so far has been to take an image and use Canny Edge Detection to get the optimal picture. From there, I do not know how I would be able to detect the distinct corners and symbols (Xs and Os). Would I use SURF to detect the grid and symbols?

It'd be great if I could find some tutorials on the topic!

I appreciate the help, tttRecognitionNoob