PNGGlitch

PNGGlitch is a small Python script that lets you corrupt PNG images without rendering them completely unreadable.

To do that, it decompresses the image first, then randomly injects errors into the file, and finally compresses it again. During the last step, PNGGlitch corrects all internal checksums and thus avoids image viewers from having a problem with the file.

PNGGlitch can be used from the command-line, or you can import it as a Python module (for whatever reason).

Download here.