I wonder if there's a way for GD/ImageMagick to detect the image data and strip everything else. (And if EXIF data is needed for photographs, import all non-binary EXIF data into the system first.)
"According to a study by the International Press Telecommunications Council (IPTC), major social networks like Facebook, Twitter or Flickr remove copyright information and other useful embedded data from pictures posted by their users"
It also compresses big files though so I'm not sure if it can do it without effecting the image data and format itself.
But it won't help. You could just make your data a real image.
They could even implement that in their TOS: "whenever you upload a photo you agree to a random byte being modified on one of the pixels on the border."