Let's consider a more complicated scenario: the connection between users and photos.
A user can post many photos. But a photo can also be connected to many users.
Putting a single foreign key in one of those tables won't suffice. Instead, we must first ponder the real-world word we use to describe the connection between a photo and a user.
How about appearance?
|45||Cookie Monster||New York|
|46||Kermit The Frog||Los Angeles|