iSteg is a free Macintosh encryption tool used to hide a file in a photograph.
http://www.hanynet.com/isteg/iSteg is an encryption tool used to hide a file (for example a zip archive) inside a jpeg picture. This encryption technology is called steganography. iSteg is a frontend for the opensource tool outguess 2.0.
iSteg can be used to both encode and decode a hidden file.
TO OPEN ISTEG IN OS X 10.8 MOUNTAIN LION AND UP PLEASE RIGHT CLICK ISTEG ICON AND SELECT OPEN, THEN CONFIRM.
http://www.hanynet.com/isteg/
https://alternativeto.net/software/isteg/about/