Re: Invisible watermarking / GD2

On Sunday 01 August 2004 07:10, Joseph Hill wrote: > I use GD for stamping images with a visible watermark - in this case, a > text string and a tracking number appended to the bottom of each image. > > However, I'd like to embed tracking information (I sometimes see my pics > crop up on mailing lists... And they're the ones I see copied!) into the > picture. > > Digimarc have a nifty looking copyrighting setup, but with a price-tag of > over three grand for an automated system, it's not affordable. Well it's their IP and they're free to make money from it. > Does anyone know how to have PHP /GD invisibly watermark images? The info > on the PHP site's GD info pages suggests this can't be done. If I'm not mistaken, the only tools you need are the ability to read the colour info of a particular pixel, and the ability to set the colour of a particular pixel. The GD lib provides functions to do both. The only other thing you need (which the GD lib does not provide) is a watermarking algorithm. I suspect google will have more info on those. -- Jason Wong -> Gremlins Associates -> www.gremlins.biz Open Source Software Systems Integrators * Web Design & Hosting * Internet & Intranet Applications Development * ------------------------------------------ Search the list archives before you post http://marc.theaimsgroup.com/?l=php-general ------------------------------------------ /* "Card readers? We don't need no stinking card readers." -- Peter da Silva (at the National Academy of Sciencies, 1965, in a particularly vivid fantasy) */