Images of three HMCGs in SDSS. The inner circles show the minimum circle that encloses all the group members (Θ_G), while the outer circles represent the radius of isolation (3Θ_G). Galaxies with spectroscopic information and apparent magnitude r ≤ 17.77 are shown as solid lines, while photometric galaxies with r ≤ 17.77 are shown as dashed lines. Upward-pointing triangles are galaxies in the same magnitude range as the CG members; downward-pointing triangles are galaxies in the same redshift range as the CG; circles are galaxies outside the magnitude range of the CG. Light blue symbols are photometric galaxies considered as non-contaminating (see text), while the bright yellow symbols are potentially contaminating objects. Objects without symbols are either galaxies fainter than r_lim = 17.77 or stars. Left: example of an HMCG without any potential sources of contamination (Group ID= 55 in Table D.1). Centre: CG with a non-contaminating galaxy within the disc of isolation whose photometric redshift is clearly outside the redshift range of the CG (Group ID= 210). Right: CG with two potential sources of contamination − one within the group radius and one in the isolation annulus− that we were not able to discard, while another photometric galaxy in the isolation annulus has been considered as non-contaminating (Group ID= 460).