The person must be in the movies or on TV (but doesn't have to be an actor/actress). The person can be specific to a role (e.g. Jennifer Elhe's Elizabeth Bennet) or just the person themself.
Please post a link to a picture of said person in the comments if you feel it would help identify the character. (For example, I can think of at least five completely separate physical representations of Johnny Depp!)
These castings can be based on things in the person's personality or on physical traits you know they have."