  While automatic computational techniques appear to reveal novel insights in
digital art history, a complementary approach seems to get less attention: that
of human annotation. We argue and exemplify that a 'human in the loop' can
reveal insights that may be difficult to detect automatically. Specifically, we
focussed on perceptual aspects within pictorial art. Using rather simple
annotation tasks (e.g. delineate human lengths, indicate highlights and
classify gaze direction) we could both replicate earlier findings and reveal
novel insights into pictorial conventions. We found that Canaletto depicted
human figures in rather accurate perspective, varied viewpoint elevation
between approximately 3 and 9 meters and highly preferred light directions
parallel to the projection plane. Furthermore, we found that taking the
averaged images of leftward looking faces reveals a woman, and for rightward
looking faces showed a male, confirming earlier accounts on lateral gender bias
in pictorial art. Lastly, we confirmed and refined the well-known
light-from-the-left bias. Together, the annotations, analyses and results
exemplify how human annotation can contribute and complement to technical and
digital art history.
