Has to be a postmark
Postmarks on a sealed envelope DO hold up in court as proof of date. So take a CD with the images and mail it to yourself. People can muck about with so called digital dates.
The kink in copyright law is: you basically have to prove that you are out more than $999 in real money before a claim (other than cease and desist of the copying) will go through a court. With a lawyer running at least $100/hr, you better make sure your 'valued' image is worth at least $1000 or more in lost income.
Low res is the way to go. You really don't need high res on the Net anyway. A low res image, even photoshopped to 300 dpi, still mostly looks like donkey doo-doo.
Hey, remember why you're taking photos anyway. If you're a commercial photog, and the photo is part of your income, being miserly is cool. If your just a snazzy amateur--heck, give it a break, already. Just be happy your stuff is *good* enough to be stolen.