Yes, you can sue them. I can recommend you the intellectual property lawer that I use. To be honest, she will charge you at least £750 if the case is settled with a few letters and phone calls. Face to face meetings with you, her and the paper will put this price up about 10 times. If it ends up going to court it will cost you up to 100 times that for all costs. Damages wise, you'd probably win £20, about the going rate for a snap in a local rag. There is no guarantee that you would win any costs back. To be honest it depends on how much you care about a point of principle. You could take it to small claims court if you think you know what you're doing.
Being realistic, you have posted a photograph on the internet on an open forum with no watermarking on the image. You have no one to blame but yourself. In these days of digital photography everyone is a "semi professional" photographer or so the chimpers (ask Wu, he'll explain) would have you believe. This is nothing but cack. Pros will guard their copyright closely, it's what puts bread on the table.
If you want to make money from your images don't play at it, do it properly and get legal advice on every contract you enter in to. If you're precious about not having your images ripped off, don't post them on the internet for all and sundry to rip off, if you do, make sure you can afford a decent lawer and are happy throwing good money after bad to fight for a point of principle. Come on, you posted it for people to look at on Twatter. People are looking at it, what's the problem?
Oh, and if it was a picture of a person (or people) other than yourself, you have had them sign a model release form haven't you?
Toodles.
