Dave, what London Headshots said about "This is what happens when you post your work on publicly accessible websites. It gets farmed for content." is right.
When you post on the Internet, you have to remember there are two different sort of people out there, there those who will find your works, thinks it's okay to copy them and display them somewhere else, as long as they leave a link or make sure they mention the credits belonging to you, then there are those who thinks if it is on the Internet, it is okay to copy them and use them somewhere else, so-what about the copyright thing, maybe they think if it's on public, it's open season.
Whichever way they do, they are wrong to copy without asking you first.
Although you mention that you're not worried as someone who used your photos left a link to your profile, which is considered to be better than nothing at all. I had took photos of my then girlfriend and posted only three photos to the Internet, but that was about 12 years ago. Recently I found those photos on the Internet, with no mention of any credits. It would seems whoever that person was, must've liked my photos, downloaded them, kept them as part of a collection on hard drive, years later, decided to upload a pick of favourite photos which includes my photos, to a website.
If you're worried, then you should consider thinking about loads of options, such as...
Post only anything you don't care if it got copied, don't post what you don't want to be copied.
Use watermarks or leave your name (or email or flick account or whatever) on the edge of the photo. (Although not really helpful as anyone can crop it off, but it's better than nothing.)
I don't have flick account or anything like that, but I assume if similar to any other websites (like Facebook), your account must've got options where you can only allow other flick members to see your photos but not open to non-members? An option to make sure that your photos don't get displayed in Google and such?
But you got to understand that no matter what anyone do, no matter what you do, uploaded photos can still get copied and displayed somewhere else, somehow.
