We present the application of Digital In-line Holographic Microscopy (DIHM) to image colloidal systems of microspheres. We show that with high numerical aperture lateral resolution of DIHM is enough to resolve self-assembled colloidal monolayers built-up from polystyrene spheres with sub-micron diameter. Owing to the two-dimensional periodicity of these kinds of structures, the Talbot self-imaging effect can be used as a measuring tool of the features of them.