Why is that important? Can the witnesses not come up with the same hypothesis and picture the suspect's face without tattoos? Going further, where exactly is t

Why is that important? Can the witnesses not come up with the same hypothesis and picture the suspect's face without tattoos? Going further, where exactly is the line here? Could police add tattoos if they suspected the suspect had temporary ones? If the suspect had long hair and cut it before the photo was taken, would it be okay for police to add similar hair to their photo? Could they airbrush out scars/freckles/etc? Change hair color? How far should we allow the police to go to make a photo look like their suspect?