Here's a relevant thread that may interest the OP
Link:
Should I Be Upset About This? | Photography Forum
Some relevant points to think about:
First thing to ask yourself is: What do you want? For them to just stop using it? To get credited as the photographer? To get monetary compensation?
For the first two, you need to realize that most folks out there don't really care or take very seriously "requests" or even "demands" to stop using your image, because they know that most people won't do anything about it if they don't comply. So, a lot of the time, they just ignore you, as it appears has happened to you in this case. And now that they haven't heard anything more about it in 6 months or so, they're feeling even more confident that it's all good and they can just keep using it with no repercussions. It also emboldens them to use others' photos for whatever purpose they want without asking any of those other photographers either.
They figure, quite correctly, that most people think that in order to legally pursue it, you'll need to put out some or even lots of bucks to an attorney up front, just like a moderator earlier in this thread stated. If you just want them to stop using it or force them to give you credit as the photographer, that's true. Attorneys don't work for free.
However, it ISN'T true as long as you're pursuing monetary compensation - the attorney simply takes his percentage cut of the settlement when the infringer pays. Not that it matters much to the infringers out there, since they know that most people believe they'll need to pay attorney fees up front, especially when people seen as authority figures like, say, a moderator on a photography forum, says it, so the photographers don't think they can afford to pursue it. Even more so when others chime in and agree that it's true you'll have to pay attorney fees up front just to get started.
While it's not actually true that it will necessarily cost attorney fees up front just to pursue monetary compensation (I've never had to pay a dime up front, as an example), with no guarantee you'd get anything out of it, it IS true that many attorneys will not take the case unless the image has been registered with the copyright office OR it was used by an entity that the attorney can expect to get big bucks from by taking the case.
In that latter case, the knowledgeable copyright attorney will get an emergency copyright registration in order to pursue the case. In your case, you gave the infringer proof via email that you knew about it at least 6 months ago and, unfortunately, you only have a limited amount of time after finding out about the infringement to file for an emergency registration. I don't recall off the top of my head what that time limit is, as it never comes up in my world - I register regularly. Related, I also never contact an infringer, as anything said might be used against my interests, so I leave it all to the attorney.
Those with concerns about others using their work without permission regularly file their newest images with the copyright office. Whether you want the infringer to just take it down and stop using it, or give you credit as the photographer, or you want to pursue monetary compensation, a registered copyright of the work gives you the legal teeth needed to keep from being ignored on the issue.
