PicSecret for Mac

From Cortic Software:

PicSecret hides secret messages in pictures by subtly altering the image in ways that are not detectable to the human eye. After a message has been embedded in an image, the image can be placed on a Web page, emailed to friends, or potentially even printed and hand-delivered in order to send the secret message. Since the secret message is hidden in the picture itself, and not simply tacked onto the image file's data, the secret message will not be destroyed by format conversion or by some modifications to the image. In addition, this makes the secret message difficult to detect by traditional means.