Lawrene is correct and even if you could as it was the way before Airbnb changed it, it would be a pretty silly thing to do, just to decline someone on his/her appearance...
Sometimes I have in Instant Book reservation from someone who does not have a protrait picture and I ask that they provide one. Usually they comply. If they did not, I would cancel the reservation as that is a requirement for me.
Actually, I did notice that if I look at my smart phone app, I see the guest picture. On my lap top computer I do not see the profile picture.
As your fellow hosts have details (thanks @Linda108@Lawrene0 and @Donna519 ) you cannot accept or deny a booking based on a guest profile image. If you'd like to learn more, please refer to our Nondiscrimination policy for greater insight @Emory2 .