Since 1846, artists have altered pictures by using paints, charcoals, and airbrushing techniques.  For example, Joseph Stalin petitioned an artist to remove Nikolai Yezhov from a photo due to his other affiliations.  Photo manipulation still happens today.  Scott Kelby definitely lays out why we retouch and use Photoshop on our photos.  By identifying that we will never look the same in 2D as we do in 3D, we will do everything we can to make sure that we look just as good in 2D as in 3D.  By having photos retouched, we hope to achieve the sensations and feelings that we experienced when viewing that person, place, or thing in person (3D).