[shawnz]

PNG is a lossless format and will not cause the image data to change whatsoever upon saving. JPEG, on the other hand, is a lossy format, but until more is known, it's impossible to say whether or not this secret data (if that's what it really is) happens to be muddled by the lossyness of JPEG's algorithm.

[markszcz]

Thanks. You got me thinking in the right direction and I found a Wiki page that talked about image formats and if they are lossy or lossless.

http://en.wikipedia.org/wiki/Image_file_formats

I found it interesting and wanted to share.