They are permitted for a couple of reasons:
- humans are a part of the biosphere and the tree of life
- it is not uncommon for users learning to use the app or site to use a selfie etc. Suspending them or deleting their records could be demotivating to remain
- it is clearly stated in the help file that while permitted, they should be kept to a small number
- the same argument about recognition, distribution could be made for many species, Mallard as an example
- anything identified as human is automatically hidden from most places on the site unless you specifically choose to search for them.