AFAIK, there is very little you can do after the fact, I would recommend placing a large watermark in the images, and reducing the quality of the images to as low a grade as possible (without making them look terrible)..
The images have to be non-watermarked, and full resolution as part of her requirements.
She can obviously prove that she created the work, and DMCA can presumably have the images removed.
My question more is, is DMCA law enough? What would you do if you were doing the same? Neither my sister or I are concerned about it however I am curious.
Prepare to be ripped off with those requirements. Its the internet look at music and films owned by multi national corporates, they cant stop it.
People will always use your stuff if you leave it open to be taken, question is are you going to spend your time making money or looking for others ripping you off?.
Watermarketing & image degrading is how any serious image provider works, why? Because it works. I would suggest you tell your sister how niave her requirements are, unles she isn`t interested in making money and is into open source art. ie. free!..
I have to agree with smartpc on this one. DMCA takedown requests could work, but alot of times the sites and their providers will just ignore you completely. It's also a US law, so I don't think the DMCA would even apply to you Matthew (or your sister assuming she's from the UK as well). So if anyone outside of the US steals her content, DMCA more than likely wont work.
If you put it on the web and it's worth stealing, it'll be stolen, simple as that...
Actually, there is alot you can do, go to court, get a decision, then enforce the decision. See, there is alot you can do, the problem is the time and money spent defending the copyrights. That is why many people or companies don't enforce it, overall, they would lose money in the long run. Sending letters can help (in a nice C+D), maybe that is enough to scare them. You can contact thier host and let them know about the infringement...
I'm an illustrator as well and there really isn't anything you can do if someone wants to steal images of portfolio sites. However, we've been told to get our illustrations copyrighted so that if it does get taken and used for profit we can sue..
This is the site your sister can get the forms at: http://www.copyright.gov/register/visual.html.
It only costs $45 and it's for as many illustrations you can fit into a disc as you want. But you can only sue once per batch. So let's say your sister has 3 illustrations (a, b and c)..
She copyrights a and b today and then later copyrights c in another batch..
If someone steals a and c then she can sue them twice, BUT if they steal a and b then she can only sue once. *edited to add: when I say sue twice I mean for the 2x the max amount instead of just the max you can sue for.
I forgot what you sue for (something damages) but we've been told that if our images are not copyrighted when we want to sue then usually they just throw the case out..
Also the copyright only applies to the US and depending on which state the infringement takes place different laws apply.
Sorry if I'm a little off topic. Hope this helps your sister though..