“I always like going to art fairs because the people that show up are pretty interesting,” says Magnum photographer Martin Parr. With his quasi-anthropological bent, the people-watching artist turns his lens on to his own artistic milieu, observing the art-world from within, during this week’s Frieze Art Fair in London.

What compels Parr to return to the art fair as creative stomping ground is the convergence of the “art world tribes, and their many different variants” in an environment which allows his creativity to flourish. “There is all this art in a white space, so you can play with putting...