Rotational invariant hash function for binary matrix

Question

I am looking for a hash function that will assign a scalar value for a small binary matrix(7x7). I want it to give different values for 2 different matrices unless one matrix is a 90 degree,180 degree or 270 degree rotation of the other one. Do you have any suggestions on how I could do this? I was expecting to find a method in image processing as this would be equivalent to a 7x7 binary image but I could not find anything.

Answer 1

Converting my comment to an answer:

If you're trying to find a way to test if two objects are equivalent after doing some sort of transformation, it often helps to pick a single "canonical form" for the object that can easily be computed. In your case, it would probably help a lot to pick a single rotation of the matrix as the "canonical" rotation and compare things that way. One simple option would be to pick the lexicographically first matrix out of all the rotations possible, then use that.