Cropping and resizing so that each subject appears to be about the same distance from the camera provides a uniform appearance to a varied group of mug shots. Eyes align and face/body occupy about the same amount of space.
Crop to Create Uniform Images Example: Cropping head shots for uniform appearance
From Jacci Howard Bear, About.com
Before: Each image was obviously taken at different times and locations. After: Even with the varied backgrounds (which could be removed) and poses the individuals appear more cohesive, as if each photo was taken under similiar conditions.
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