I don't know that there is a site that provides the online service, but pretty much any graphic designer with Photoshop (for example) can help you with the task. Check out craigslist for "services > computer" or "services > creative" ... or wait for someone here to PT you.
Or get a "photo" program, if you didn't get one with your digital camera software (Adobe makes something called Photo Editor which is much less expensive than Photoshop and probably does the job perfectly) and give it a try yourself. It's one of the easiest photo manipulations, just make sure to save a backup copy of the file so you always have an original to go back to as you learn your way around.
EP, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS