I hired an artist to create some pictures. The artist took already made pictures from various online sites created by others and sold me the pictures as their own creation. I have evidence of this with the original pictures and the ones sent to me.
Which laws has this artist broken?
Depending upon the full facts, there may be multiple legal 'harms' for which various avenues of recourse may be sought. Tricia Dwyer, Esq., Minnesota Civil Law, Minnesota Contract Law.
Much more would have to be known about your contractual agreement with the parties. Nonetheless, it would certainly appear that the "artist" may have violated copyright protections available to the owner of the photographs.