Picture frame?

[REAPER]

Any ideas how to put a border ir picture frame around a poster to make it stand out?

[Nichronos]

An easy way to frame posters is to scale up a generic poster with a good complimentary color like black or white, put it on the wall first, then put the poster you want framed on top of first one.
You'll need to finagle it a bit to center it properly, but it should give you the framed look you're going for.

[Galactic Starman]

You can flip a poster (or other items) that have a flat plain back. Then place a picture poster (front facing) on top. Thicker items can give the illusion of a bevel.

If you have posters or other items that appear to sink beneath the surface of wall or other objects. You can place a wire over the chosen position and place the object on top of the wire. The wire might be deleted or left in place as they can be hidden.