Other factors can also weaken 
or destroy the illusory effect. If 
the texture of the photographic 
image or the surface of the 
painting is visible, it will lead 
to the perception of an ordinary 
picture on a surface. If the 
picture is nearby, oculomotor 
or retinal disparity cues may 
inform observers of the 
presence of a flat picture 
surface, or the frame of the 
picture may provide this 
information. Pozzo was able to 
circumvent all these problems 
because the ceiling was roughly 
100 feet above the floor. 
Spectators do not perceive the 
surface of the ceiling as such, 
even viewing it binocularly.

    Pictures of this kind, 
pictures that are not perceived 
as pictures, are remarkable 
achievements, tributes to the 
great skill and knowledge of 
their originators. They are also 
acid proof of the efficacy of 
pictorial cues. In such 
pictures, nonpictorial depth 
cues either are absent or 
contradict the pictorial cues; 
yet the scenes depicted appear 
vividly three-dimensional. 
Among works of art, however, 
trompe l’oeil productions are 
exceptional, and perception of 
them differs from the 
perception of other pictures. 
Even within the domain of 
aesthetics it can be argued that 
trompe l’oeil productions are 
not really examples of 
paintings qua art. For a 
painting is meant to be seen as 
a painting, as representing 
something else but at the same 
time as an object unto itself.