Using stock images from others but with correct citations?

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?

The only real way they would know is if they took down what websites it was used on. Not sure.

hmmm....bummer. I would really like to know if the companies have a way to find out. If not, then these companies will most like go bankrupt if people just steal and quote/cite the images properly. Or am I missing something?