  Spontaneous downconversion is a versatile source for correlated biphotons
that has been employed in many quantum sensing and imaging experiments.
Spatially-resolved photon-counting detectors allow to access a large number of
modes, posing the challenge of an accurate description of such systems. We
propose a simple model to generate images as though acquired by a
photon-counting camera, and allow to simulate and characterise the detection of
quantum correlations. We derive quantitative parameters characteristic of the
spatial correlations for a given experiment, comparing the images produced by
our model to the frames acquired by an electron-multiplying CCD camera.
Moreover we accurately predict the decreased detection of spatially correlated
biphotons caused by introducing a variable amount of optical loss after the
nonlinear crystal, even though the total number of detected events is kept
constant, showing excellent agreement between model and experiment.
