If one closes one eye pictorial relief deepens, if one superimposes the eyes with an optical trick it articulates even more. We have developed methods to probe pictorial relief with sufficient resolution to be able to study its geometrical structure in detail. Repeatibility can be quite good and the responses are typically fully consistent. However, they are typically nonveridical.
Different observers yield results that are more like each other than like the object depicted.
I will especially address the influence of viewing conditions.