Copyright issues are a hot topic for the Internet.
If you own a Professional level camera there is a facility to embed copyright information in every images you take in the menu options.Professional photographers who do not use methods of securing their property probably leave themselves open to missuse.
If you create an image from scratch, you can embed "PLUS" copyright information. When you prepare an image for display on the Internet (as all must be at least resized) it is a trivial process to type the ASCI code (hold down the alt key whilst typing a set of numbers) alt 0159 for the Copyright symbol.
You then use the blending and bevel tool to 'raise' the symbol and make it transparent. Make it as big or as small as you like and you have your copyright warning on the images. CS5 of photoshop will remove it in about 5 seconds!
I dont want to underestimate the problem of protecting images from unauthorised use but writers have been faced with palgurism for far longer than photogrpahers with copyright issues. Are there any less articles being written today because of their problems? Nor are any less photos being sold today because of misuse of copyright.
Put in the proper context, perhaps the top 10% of images we (the Professional photographers of the world) take are really valuable enough to need protection. The best protection of all is not to display them but an alternative I've found useful is to photograph a print of the valuable work at a 45 degree angle with a wide aperture. Copying photos with a portion of it out of focus and with a distorted perspective is far harder than cut and past one off the screen.
IF you place a person near the image for effect, it also reinforces the fact prints of valuable proportions actually exist and the picture is not just an image from a storage of images. I don't know of too many photos worth protecting by enforcing copyright that have not previously been sold. For anything to have value, it needs a market to decide on that value.
Otherwise those who complain the loudest of the potential for copyright violation IF they join a site, are probably better off not exhibiting their work in the first place. ANd then there are sites set up to crawl the INternet looking for violations of your images. Some are free some you pay for but all will turn up unauthorised use of your images. How you proceed after such a discovery is another matter all together.