Hi,

That's a bit ambiguous.

1. Do you want to make a movie of a person or other 'object' that appears to show the object (usually called the 'subject' in this context) against another background, such as a desert, ocean, etc?

If so search (here, or better on Google) for green screen.

In short, you just record the movie with your subject in front of a bright, evenly coloured green screen/wall/cloth/etc. You don't say what product you're using; presumably you didn't read the post at the top of the forum page. But in MEP MX for instance you then use Effects > Video Effects > Chroma Key > Green.

2. Do you want to work with an object already imported into MEP and change it so that the 'object' appears against a new background, like the examples above? If so, is it a movie clip or a still image, such as a photo?

2a. For the latter you need to search for masks, but it would be much easier to do the job first in your image editor.

2b. For a movie clip, it depends on the extent of the motion. For example, it should be possible to make a subject sitting and just talking, to appear in front of an ocean beach view. But if the subject got too excited and moved any part of its head or body significantly, then the deception would fail.

Or do you want something else not covered above?

--
Terry, East Grinstead, UK