A remover plus a compositor cuts the subject out along an alpha edge, then drops it onto a new layer still carrying the light it was shot under. Put an office-lit person on a sunset beach that way and the mismatch shows in under a second.
Regenerating the scene works differently. The environment is built with the subject in place, so the key light lands on the same side in both, its colour spills onto skin and packaging, and a contact shadow appears where the subject meets the surface. Glossy surfaces also get a soft reflection.
The edge is the other tell. With no alpha matte to feather, hair and fabric are drawn against the new scene rather than trimmed out of the old one, which removes the usual halo.
Perspective is the first failure. A subject shot from below, dropped into a scene rendered at eye level, reads as wrong however good the light is. Match the camera height you ask for to the one you shot at.
Hands, small text, dense patterns, fine hair, glass, and strong reflections are harder than a plain shoulder or a matte bottle. Labels usually survive; six point legal copy sometimes does not.
The subject is occasionally reframed or rescaled slightly: we saw it once with a wristwatch that came back a few percent larger. We do not promise the subject returns untouched, or that a run works first time.
Re-running is the fix, with a tighter description or a different preset, and each re-run is a fresh 20 credits. This is also a still image tool: no video path, no batch queue, no layer file.