A retroemission device (REM) is an incoherent holographic device that represents a lenslet array situated on a substrate containing fluorescent material. Each lenslet focuses each wavelet of an optical wavefront incident on the REM device into a diffraction-limited volume (voxel) in the fluorescent material, so that the voxel coordinates encode the angle of incidence and curvature of the wavelet. The back-propagating fraction of the excited fluorescence is collected by the lenslet and quasi-collimated into a back-propagating wavelet. All wavelets are combined to reconstruct the incident wavefront propagating in the backward direction. We present a theoretical model of REM based on Fresnel-Kirchhoff approximation describing the reconstructed 3D image characteristics versus the thickness of the fluorescence film at the focal plane of the lenslets. Results of the computer simulations of the REM-based images of a point source, two axially separated point sources and an extended object (a circular rim) situated in the sagittal plane are presented. These results speak in favor of using a fluorescence film of minimum diffraction-limited thickness at the lenslet back focal plane. This REM structure minimizes the fluorescence background and improves the 3D imaging resolution in virtue of the exclusion of out-of-voxel fluorescence contributions to the reconstructed wavefront.