A face annotation object contains the results of face
The bounding polygon around the face. The coordinates of the
bounding box are in the original image's scale, as returned
in ImageParams. The bounding box is computed to "frame"
the face in accordance with human expectations. It is based
on the landmarker results. Note that one or more x and/or y
coordinates may not be generated in the BoundingPoly
(the polygon will be unbounded) if only a partial face
appears in the image to be annotated.
The fd_bounding_poly bounding polygon is tighter than
the boundingPoly, and encloses only the skin part of the
face. Typically, it is used to eliminate the face from any
image analysis that detects the "amount of skin" visible in
an image. It is not based on the landmarker results, only on
the initial face detection, hence the fd (face detection)