I had a model release form that was rejected because Shutterstock says that it has 2 different ink colors on the form, which to them means that the witness signed it on a different day than anyone else (which is of course not true). he just used a different pen on the same day.

If its a jpeg just desaturate and resubmit.

Suddenly SS rejected a property release they always accepted -- also was clear it was property of photographer.  At a loss.