A must-read post for designers, and he references a book I’m embarrassed to say I don’t own yet, Understanding Comics by Scott McCloud:
The image on the left is a face of a specific person. The image on the right is the concept «face»; it could be any person. When designing user interfaces, we rarely ever want to show a specific entity; typically, we want to convey an idea or a concept. Details can easily distract from that idea or concept.