@Sheila175 one way to handle it is to write to the guest one more time, saying very clearly and explicitly that you require a photo that includes a clear image of their full face. Include an explanation that if the guest does not provide the required photo, then the reservation will be cancelled within (your choice) days.
Also contact Airbnb support; tell them you require a photo of the guest's face, and that you have asked the guest more than once to provide the photo. Ask Airbnb support that if the guest does not provide the photo with (your choice) days that you would like a penalty-free cancellation of the booking.
Follow up in (your choice) days with Airbnb support if the guest does not provide what is required.