PHP-Steg - www.puremango.co.uk

This is application is totally insecure(*) and is a 'concept' application rather than something to actually be employed for security.
Download the source code here.

Image		- jpg for encoding, png for decoding
Hide file		- leave blank if you're just decoding

* - for explanation, see the PHP-steg page on puremango.co.uk (under projects)