Two dimensional decoupage is where pictures are glued onto a hard surface and varnished to make it look like it was painted on. It started way back when people couldn't afford to have painted furniture so they got their carpenters to hand colour black and white prints and glue them on. Then enough layers of varnish are added to embed the paper so deep that it no longer looks like paper.
This is a 'before' example of a print:
And this is what it looks like after colouring:
It is particularly good on country furniture like this old rocking chair:
Here is a close of of the detail. This one hasn't had the full treatment of varnish yet:
It is also a nice treatment for sprucing up wooden tissue boxes: