Lost In The Woods

Photographically speaking that is, these trees hardly constitute as "woods".  

I had the odd experience of scrolling through FB and seeing an article appear, headed by one of my photos. It's a funny feeling, recognition was the first thing.... a sort of "that looks familiar" instantly followed by "sodding hell, that is my photo" and then...."how the hell did it get there?". It's not that amazing, I have sold about a dozen JPEGs to the tourist website Visit Copenhagen (for about £200) but I did so on the understanding that it was for their own websites and library, for the promotion of Copenhagen. So it seems that they offer their library to anyone, for free, if it is for the promotion of Cph. 
So; how do you know who's using your shot and when does it become commercial use as opposed to promotion? Should I be worried? 

The same photo showed up here.