Here is a blog post on how to do a simple Droste effect. I use Pixelmator, but of course Photoshop, Affinity, The Gimp, and lots of other tools work just as well. (Note that this is a Droste-like effect. For a true, algorithmic Droste, you need other tools.)
http://kallokainphoto.blogspot.no/2014/09/droste-effect-with-pixelmator.html
