Picrypter

Picrypter is an encryption tool for 24-bit image files. This program uses the unique keys to encode/decode pictures. To make a picture hidden, Picrypter encode every single pixel of an image. In fact, it changes the color of them. The result is the indecipherable dump of pixels. So, the encoded file is still an image file and can be viewed in any picture viewer or editor. After decoding, the picture gets back without any distortion.

The only disadvantage is that the encoded image can be saved only as a bitmap file. It cannot be compressed as JPEG or other picture compression format, because after compression the pixels' colors are some changed and thus cannot be decoded without distortion.