system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do CGI artists know what's behind the objects they remove in live action movies?
gpt
Copying parts of the background if it is visible at any point during the shot (most common, also mostly automated process at this point)

or

Using a reference shot. Basically they film the scene several times with some elements simply not there, for SFX background references

or

If all else fails, rotoscoping. Painting shit out frame by frame.