For regression testing display data, would it be possible to analyze and test buffer output from OpenGL?

I want to regression test an embedded display, but testing the code won't suffice, and pixel-by-pixel comparison is far from perfect. Instead I'm thinking about testing the raw data used to render the image, i.e. reading from the OpenGL buffers.

Would the data still vary regarding anti-aliasing, decimal precision, pixel density etc. or would it be bit-by-bit copy of previous buffer/render?