I have raw image data that is XOR-encrypted with a fixed-size one-time pad repeated over the length of the image. I know what the format of the image data container is so I can successfully retrieve the first 6 bytes of the key.

But that's it so far, I have no idea how to proceed.. Are there relations between adjacent pixels? Has any research been done on the subject, and if there is, how? I've searched for hours to no avail.