So I just asked my Mexican colleague here at work, just to double check, and pretty much it's as so:
So yeah, La pintura is more specific, but still has multiple meanings - it's even more literal than you would think. It can mean the painting that someone did of a landscape or whatever, but it can also mean the actual paint that someone used on a wall, or that is in a tin, whether it's dry or wet.
El cuadro is the picture with the frame, or just the frame, or lots of other things that don't necessarily have anything to do with what you hang on your wall and admire.
According to the RAE, "el cuadro" is " 1. "a flat figure surrounded by four straight lines 2. a rectangle. 3. The frame of such a picture (of a cuadro) 4. and more...
A "pintura" is 1. a painted work 2. an art painting 3. lively, animated verbal description of people or things. 4. Etc., and more
"Marco" is (also" "a picture frame." Also, that which surrounds, supports a structure (such as a sculpture, or paining) or door, or window, etc. (framework?)
painting NOUN 1. (picture) a. la cuadro m, pintura (f)
- (activity) a. la pintura (f) painting and decorating - pintura y decoración
NOUN 1 (Art) (picture) cuadro (m); pintura (f); (activity, genre) pintura (f) to study painting estudiar pintura; French Impressionist painting la pintura impresionista francesa See also - oil