Can you composite and matte-paint over these nature scenes? – Curated Nature Scenes

Yes. Editing is unrestricted for any use the licence permits, and matte painting over a plate is exactly the sort of derivative work the licence exists to allow.

The two limits

You may not distribute the edited image as an image; heavy editing does not create a file you can licence onward. And you may not present a real, identifiable place misleadingly as a factual record. Design and drama are unrestricted; the line is a claim of fact.

Plane separation

The first question on any plate is whether it comes apart.

Frames with atmospheric perspective — fog, haze, mist between ridges — separate almost by themselves, because depth is already encoded as contrast and colour. A luminance-based extraction gets you most of the way to clean planes.

Flat, evenly lit scenes with no atmosphere are much harder, and no amount of rotoscoping fully substitutes for having chosen a better plate. Search the atmosphere tags first.

Sky replacement

Match the light direction before the colour. A valley lit from the left under a sky lit from the right reads as wrong instantly, even to people who cannot articulate why.

Check the horizon boundary at 100 per cent. Automatic selections leave a halo along treelines and ridgelines that is invisible at fit-to-screen and glaring on a large display.

Extending the frame

Generative fill and content-aware extension work well on sky and water, adequately on distant terrain, and badly on anything with recognisable structure. Extend the top of a frame freely; extend the foreground with suspicion.

If you extend, do it before you grade, so the invented region takes the same treatment as the rest.

Grain and integration

The single most effective integration step is matching grain. A clean still dropped into grainy footage reads as a still no matter how well it is graded; adding matched grain fixes it in one operation.

Add grain last, after the grade, at the delivery resolution.

Bit depth

Convert to 16-bit before grading rather than after. The precision does not recover information, but it stops each adjustment from quantising the one before, which is where most sky banding actually comes from.

Records

Keep the layered project and record the asset ids in it. A composite built from four licensed plates is four licences, and knowing which four when the clearance schedule is compiled is worth the ten seconds it takes now.