3D Painting

Could you just use spackle/joint compound over plywood or OSB, maybe? Or even actual plaster?

Papier mache might be something to try, too--the paper might make it easier to make the sorts of humps and bumps you want, and once it's painted over it could have the sort of "fuzzy" look of the ref image.

Then just paint it. That's what I would think, anyway. I hope that helps!

Let us know what you decide, and keep us posted. I'd love to see what you come up with in the end!

(ETA: I guess you mean more like what technique would be used. Were it me, I'd do one straight base coat of plaster, and then use a trowel to add more in random diagonals, followed by putting on gloves and shaping the exact valleys and hills with my hands. Maybe I'd do a solid coat and then do almost like a knockdown texture without the actual knockdown part--basically throwing handfuls of spackle/plaster at the wall, but shaping it up or rounding it off instead of knocking it down with a skimcoat tool, do you know what I mean?

Sidgirl, I have used 3-D painting and green screen.

What have you used?

@User I haven't used either of those. Why do you ask?