11-04-2020, 07:24 AM
Cutting out with a path as indicated is an essential first step, if this is done right, the rest is comparatively easy. Windows have to be handled properly (replaced with something with partial opacity where details of the original image background have been removed).
The real difficulty is finding a background with the same perspective and lighting direction as the car, and where the reflections on the car don't look out of place (for instance, your Mercedes picture has been shot in a place with light fixtures on the ceiling, so they don't go well with a desert). You may also have to add new reflections on the car.
Last, the car normally casts a shadow somewhere on is background (especially around the wheels, where proper shadowing is what makes the car look firmly put on the ground).
TLDR; 80% of the problem is not Gimp....
The real difficulty is finding a background with the same perspective and lighting direction as the car, and where the reflections on the car don't look out of place (for instance, your Mercedes picture has been shot in a place with light fixtures on the ceiling, so they don't go well with a desert). You may also have to add new reflections on the car.
Last, the car normally casts a shadow somewhere on is background (especially around the wheels, where proper shadowing is what makes the car look firmly put on the ground).
TLDR; 80% of the problem is not Gimp....