Now I truly understand copyright infringement..

[KmH]

As some have said, don't post it online without a water mark if you don't want people to use it.
you can always lower the res for the web (even 800x600 is totally viewable)

Watermarks are useless (crop/clone) if someone wants the photo bad enough, and many copy them watermark and all.

There are many ways to up-res a photo.

There is only 1 sure way to keep people from taking your photos off the Internet - Don't put them there in the first place.