I'm jumping in a little late here, but I want to comment on copyright laws. Like Alan said, as soon as you put any work of art in a physical form (ie a print for photos, typed out on paper for stories, sheet music for a song, etc), it is automatically, legally copyrighted in your name. That said, you can register your work with the copyright office. It's been a while since I looked at the prices, but I believe it's $35 per indivitual photo -or- you can copyright a collection of photos (they just have to be under the same title - ex: "Chelle's photos 2004 - 2005") for, I believe, the same price. The benefit to registering is if there ever is a legal dispute, you have proof that that photo actually belongs to you as of a certain date. Otherwise it would be difficult to prove (unless the photo was published somwhere under your name with a date) who it actually belonged to since you both could roduce copies of the photo.
Also, just something to keep in mind. Any time you photograph personal property that is not on public display (like a pic of a personal residence or someone's dog), you really should get a property release which baically states that the owner has given you permission to photograph their property. Likewise with people. Anytime you take a picture of a person (I believe they have to be recognizable, so if it's something like a sillhouette or their back, it doesn't apply), you have to get a personal release saying they gave you permission to take their picture.
If they are photos for your own private collection, then it's not too big of a deal, but if you ever want to sell, publish, or publicly display those photos, you really should have those releases.
As for keeping people from stealing my photos, I'm just really picky about which ones I make available online. I also never put any high res pics online. I used to keep them below 600 pixels wide/tall, but I've recently inched up to 640. I don't post anything above that, though. So even if someone did save my pic, they wouldn't be able to get a decent print out of it. The only thing anyone's ever stolen from me and used online (that I know of at least) is an avatar with my oscar (why someone would want an avatar of a fish that's not theirs, I don't know). I asked him to remove it and he did. He told me he found it on another forum, but I went there and didn't see it anywhere.
EDIT: It's $30 to register. Info here:
http://www.copyright.gov/register/visual.html
And also some info here:
http://www.piercelaw.edu/tfield/copyVis.htm
-Chelle