Question about layers

hi guys need your help helping a friend with a project he gave me some footage and wants me to cover a sign with a picture its a character holding a sign he wants me to cover the sign the character is holding I’m doing this with motion tracking because the character is moving while holding the sign and its working good so far but he says it doesn’t match the grain something like that he wants me to cover the sign with the picture but the backround is black that’s the problem is there a way around this?sorry for the confusion.

It is hard to understand from your description, what the problem is that you want to solve. Missing grain on sign? Black background? Sign not showing? Something else? At least post an image of your current setup, so we can see what you are talking about.