A friend of mine gave me his pack of stock images that he legally purchased with all the proof. At that moment I realised that I could actually just take the images from his website and use the citations he had been using all this while. Theoretically it would seem that I would have bought the stock images as well. My question is, how would anyone (especially the stock image provider company) know whether the images I use are legally purchased or are stolen from other websites although properly cited? Any ideas what could happen?