A lot of police departments do mugshots like that now - draping a towel to conceal the shoulders and chest. I suspect it's to clean up the "photo lineup" results in the future - nobody will be subconsciously focusing on clothing.
For the FBI facial recognition database...
Local practice is to put a towel around their neck to keep defense attorneys arguing that neck tattoos are prejudicial in photo lineups.
They do it for all defendants processed in the county.
Not much they can do about face tattoos.