Just to be clear to people not following the link: physical 3D models. But today you could also make electronic 3D models (in, say, Blender) and shoot them from various angles to get sprite images. Later 3D-looking sprite-based games did this.

I assume they rotoscoped over those photos because the images are definitely look hand-edited. Blizzard went similar for Starcraft and Diablo - start with 3D model renderings and then hand-paint over them to get the art pixel-perfect.

They were definitely hand-edited and de-babelized. Would be interesting to have high-res images and edits for the later versions of Doom ports for today's screens, considering Doom ran on a 320x200x256 display.

High-rez Doom sprites were actually made for one of the later ports of the game - N64, I think.

Doom 64 ran at 320x240. :D The sprites are higher res so it looks better when scaled up close, but in the end no different than plain old DOS doom.