Honest question: aren't ACTA and the like all about cross-border copyright enforcement? I can't say I'm an expert, but...
Note that it's your friend claiming copyright infringement, with an exclusive license in hand. Legally, the question is whether you can actually give an exclusive license after uploading a photo to Facebook (the ToS has been challenged and changed on similar issues), but that is not between your friend and Facebook.
Google "facebook dmca": Facebook will happily take pretty much any page down (e.g. http://www.techdirt.com/articles/20101007/01244411320/facebo...). Do you really think that Facebook is going to risk a court case where it has to prove (on its own dime!) that you actually did have copyright on the image when you uploaded it, risking its DMCA safe harbor status?
I'm also not an expert, but we've had cross border copyright enforcement for over 100 years with the Bern Convention. The UK will recognise and enforce USA copyright that happens in the UK.
Facebook has to take down DMCA requests to stay with the DMCA and the safe harbour rules. However that's a US law. I don't know if non-USA people can invoke it.
Note that it's your friend claiming copyright infringement, with an exclusive license in hand. Legally, the question is whether you can actually give an exclusive license after uploading a photo to Facebook (the ToS has been challenged and changed on similar issues), but that is not between your friend and Facebook.
Google "facebook dmca": Facebook will happily take pretty much any page down (e.g. http://www.techdirt.com/articles/20101007/01244411320/facebo...). Do you really think that Facebook is going to risk a court case where it has to prove (on its own dime!) that you actually did have copyright on the image when you uploaded it, risking its DMCA safe harbor status?