Theres a somewhat cult/popular wrestling promotion management game series thats been running since 2004/5, which because of licensing, takes place in a fictional universe with invented wrestlers with profile photos created with 3d rendering programs. In the online forums they're called renders.

The online community has made countless mods for the game that mimic real life wrestling scenarios/promotions and use real images of wrestlers like those used for this poster, but because of the established shorthand of "render" to mean "a wrestlers portrait pocture" people started referring to these too, as renders. This then spread to other internet wrestling forums like here. People would complain they're not renders, then people make fun of them for complaining and decide to use the word more.