zett - 6:35 am on Mar 30, 2012 (gmt 0)
That said, you cannot sue without registering your rights with the same office (copyright.gov)
I don't think this is correct.
Your work is protected as soon as you create it. You own the copyright in your work (except for parts of the work where others hold the copyright).
So you CAN sue for damages at any time without registering your work with the US Copyright Office. This is even more true when you are living abroad and creating works. You do not have to register your works with the US Copyright Office to have the copyright for your work.
But unfortunately, this will only allow you to sue for ACTUAL damages. Say, you licence photos at 100 US Dollars each. Now you come across an unlicenced use of your image. You can sue the infringer for actual damages, i.e. the amount that your works typically sell for. So you might sue for 100 US Dollars plus some damages (50 Dollars) plus attorney fees. In the end, you might get 150-200 US Dollars out of this infringement. Good, but it can be much better!
That's why smart content owners register their works with the US Copyright Office: THIS allows you to sue for STATUORY damages. And these range from $750 to $150,000 PER INFRINGEMENT. Five images - five infringements. Doesn't that sound much better? (And this explains why Youtube and the like are soo afraid of copyright infringements, especially when the rights holders are Hollywood studios with very deep pockets.) This can become quickly expensive, very expensive.
Having said that, I am not a lawyer, so YMMV. Go check with an attorney specialized in US IP Law. That will give you a full view of your options.