eli5: How can sites like Getty images own/sell historical images

Question

I am doing research over WWII and I have noticed that stock image sites want to charge 200USD per image to use them in an educational manner. How do they get the copyright to these images? It makes me afraid that a handful of sites own the rights to most of the historical images and videos now.

In: Other

Answer 1

People sell images, often when people die and the families don’t know what to do with them and Getty and other places buy them at auction.