Other effects have a similar 
explanation. Consider, for 
example, the case of objects 
depicted as jutting out toward 
the observer, for example, a 
snapshot of someone reaching 
straight out to wave at the 
photographer. Viewed from the 
side, the arm still seems to 
reach out toward us. If we 
viewed a real arm outstretched 
in this way from the side, it 
would project quite differently: 
as we moved to the side of the 
real person, the projection of 
the arm would become 
increasingly horizontal. But 
when we view the picture from 
the side, the orientation of the 
arm in the picture remains 
more or less unchanged, and we 
continue to see the arm
pointing toward us.