mocha Pro would use the background track tries to
replace the selct foreground object with clean areas from the
background (from other frames in time). Also employs some
intelligence to matching the lighting, etc. This can be very
successful if the background is non-organic and there is enough
parallax camera movement. In cases where the foreground passes
multiple "planes" each bg plane needs to be tracked on their own
layer.
When the clean frame does not exist in the shot at
all, the artist can feed the module clean, painted frames.
These clean frames can be interpolated into the shot and even
mixed with the auto removed frames.
There is a little learning curve, but I would
suggest watching Mary Poplin's Remove Module tutorials that
cover clean plates.