SAFR can detect and report when people are attempting to hide their presence by partially occluding their faces. (Note that SAFR is usually able to successfully detect and recognize faces even when subjects are attempting to occlude their faces.) 

It's important to understand that the occlusion percentage that SAFR reports represents the confidence level that occlusion is occurring. The percentage does NOT represent the percentage of the face that is covered. For example, holding a pen over your mouth will often report an 0.8 or 0.9 value for occlusion. That is, SAFR is reporting that there's an 80% or 90% chance that you're trying to occlude your face; obviously the pen isn't obscuring 80%-90% of your face. Currently there isn't any mechanism to report the percentage of the face that is occluded.  

The REST APIs and SDKs provide a list of face features which will could be used to ascertain if the mouth, nose, or eyes are occluded. (This information isn't exposed in the SAFR Desktop Client user interface.) Mask reporting can be used to ascertain when the mouth and nose are occluded.