Daniel Cremer wrote:

> Hi,
> 
> Are there any libraries for ruby that do invisible watermarking on
> images ? If not, does anyone know of a good C library that could be
> ported to ruby.
> thanks,
> -Daniel

RMagick (http://rmagick.rubyforge.org) includes a `stegano' method, which
can be used to embed a watermark in an image. It's uses are quite limited,
however. Only lossless RGB format images, such as PNG images, can be
watermarked. The stegano method does not work with GIF (pseudocolor), or
JPEG (lossy) images. Once watermarked, the image cannot be edited in any
way or the watermark will be destroyed.

AFAIK, "industrial strength" steganography, such as that offered by
Digimark, is expensive and commonly uses patented techniques.