One of the major challenges in modern astrophysics is to understand the origin and the evolution the bright, massive early type galaxies (ETGs), since there are likely to be good probes of galaxy evolution, star formation and, metal enrichment in the early Universe. In this context it is very important to set up a diagnostic tool able to combine results from chemo-dynamical N-Body-TSPH (NB-TSPH) simulations of ETGs with those of spectro-photometric population synthesis and evolution so that all key properties of galaxies can be investigated. To this aim we adopt the galaxy models calculated by the Padova group in two different cosmological scenarios: the standard cold dark matter cosmology (SCDM), and the so-called Concordance cosmology (CDM, with = 0.762). For these template galaxies, we recover their spectro-photometric evolution through the entire history of the Universe. We computed magnitudes and colors and their evolution with the redshift along with the evolutionary and cosmological corrections for the model galaxies at our disposal, and compared them with data for ETGs taken from the COSMOS and the GOODS databases. In particular we focus on the creation of artificial images that resemble two-dimensional distributions of luminosity from which we derived the structural and morphological parameters of the simulated galaxy. In addition to this, we address the question of the scaling relations, and in particular we examine the one by Kormendy. The theoretical results are compared with observational data of ETGs selected form the SDSS database.