hi jmr -
there is a ton of information on copyright protection on http://www.editorialphoto.com .
i was always under the impression that as soon as you created an image it was copyrighted, but within the last month or 2 i came to realize that while the image *is copyrighted*, since it isn't registered with the copyright office, there aren't really many lawyers that will help you out if you run into a problem of stealing & usage ... registering isn't very hard. you fill out an application, and submit the images & a fee of $30 for a group filling. within 6 months you will get notification that your work is registered. ( if people decide to take your images and use them without your consent, there is a pretty steep fine for each offense --- and from what i was told by the copyright office, you can't really take anyone to court without the certificate. )
there is way to electronically tag your work. it is through digimarc (http://www.digimarc.com/ ). there is something that is imbedded in the image file - digimark has "spyder-bots" or something else as wacky sounding that scrubs the internet looking for your work. it isn't very expensive and from what i understand it is very much worth it.