I've had this happen to me before. It was a 
little annoying that the fan artist didn't bother 
to contact me first. I probably would have OKed 
it. Other than the rudeness, it didn't bother me 
that much. I have seen a few stolen scans of my 
cels before the fan cel issue came up, so I guess 
I was rather resigned to it by then. I just 
stopped putting up anything really expensive or 
that I really didn't want stolen.