I don't know how many of you are interested in a way to digitally watermark your photos, but I have found a combination of open source software (free) and some self made Perl wrappers that allow you to hide as much data as you like in an image. The applications required are:
CYGWIN -Cygwin is a Linux-like environment for Windows. It consists of two parts:
A DLL (cygwin1.dll) which acts as a Linux API emulation layer providing substantial Linux API functionality.
A collection of tools which provide Linux look and feel.
PERL - Can be part of the CYGWIN install
STEGHIDE -Steghide is a steganography program that is able to hide data in various kinds of image- and audio-files. The color- respectivly sample-frequencies are not changed thus making the embedding resistant against first-order statistical tests.
SOME PERL scripts that provide a friendly interface to STEGHIDE.
I won't put any more detail in until I see if anyone is interested. It's not what I would call a simple process to set up all of this stuff, but if you are into hacking stuff, you might like this. It is free and legal.
Don