What's wrong with filling a database; that's what it's for!
Unless there is something unique about each of the 5 images (ie, the first is always the user's profile picture, the second is their car, etc...) then I think the way you have it implemented now where a User hasMany Image and images are on their own table.
You just have to implement a little logic to maintain the 5-image limit is all (count $user->images as a validation before storing)