SDSS-DR17 three-colour images of four selected SIT systems (SIT 86, SIT 222, SIT 217, and SIT 17 from upper left to lower right). This is an example of the morphological category classification: a) the system is composed of three spiral galaxies (TL, upper left panel); b) the system is composed of three elliptical galaxies (TE, upper right panel); c) the A galaxy is a spiral galaxy (TCL, lower left panel); and d) the A galaxy is an elliptical galaxy (TCE, lower right panel). North is up and east is left. The image scale is 0.215″ pixel⁻¹, and the centre of the image represents the A galaxy.