This is MINE!!

I was notified by a Princess about 6 weeks ago that a business was using pictures of my dresses to sell their own dresses. In one look I knew exactly which customer they had stolen the pictures from! I let her know and now it's up to her to prove they are big fat thieves! They do not have my particular pattern and technically they have done just what I did, take a look at a picture and make a dress off it. However this company advertises heavily on Facebook and just about every time I'm on there I see MY WORK being advertised as their own. it really stinks! I'm going to see if there is anything else that can be done, maybe I can sue them...