Including author information in JPG

How do you include information about the author in a common .jpg file

[EvilPenguin]

Hi,
I've got some issues about .jpg. I'm running quite a large site where many people post their documents. Due to certain restrictions concerning the contents of these documents, I'd like to be able to know WHO posted them. With Word or PDF docs this isn't a problem. But I don't have any idea how to include information about the author in a jpeg (something like the author field in word that you get when you view the properties of a word documents).

[edit_g]

If you're using photoshop you should be able to use filter/digimarc and "embedd watermark". You can add your name and copyright info here, which can be read using the "read watermark" feature under the same menu.

Unfortunately digimarc charges money for this, i.e. you have to register....

You could also try these (free) tools:

[alpvision.com...]

[graphicssoft.about.com...]