  We consider the relative configurational entropy per cell S_Delta as a
measure of the degree of spatial disorder for systems of finite-sized objects.
It is highly sensitive to deviations from the most spatially ordered reference
configuration of the objects. When applied to a given binary image it provides
the quantitatively correct results in comparison to its point object version.
On examples of simple cluster configurations, two-dimensional Sierpinski
carpets and population of interacting particles, the behaviour of S_Delta is
compared with the normalized information entropy H' introduced by Van Siclen
[Phys. Rev. E 56, (1997) 5211]. For the latter example, the additional
middle-scale features revealed by our measure may indicate for the traces of
self-similar structure of the weakly ramified clusters. In the thermodynamic
limit, the formula for S_Delta is also given.
