Issue with test set in CASIA-SURF HLDI
https://gitlab.idiap.ch/bob/bob.pad.face/blob/master/bob/pad/face/database/casiasurf.py#L178
'unknown' is not needed anymore right?
Also https://gitlab.idiap.ch/bob/bob.pad.face/blob/master/bob/pad/face/database/casiasurf.py#L44
the .attack_type
labels.