Example:
User A (id=10) has created a photo resource
photo: (id: 1 user_id = 10, url: \"http://...\")
If CanCan is too advanced, you should loon into checking the id of the accessor in the controller using...
if @user.id == @photo.user_id # edit photo details else redirect_to root_path, notice: "You! Shall! Not! Edit!"
...or something like that