Sommer worked in all formats: large, medium, stereoscopic, cabinet and carte de visite, and was skilled in portraits, views and reproduction of works of art. He was one of the first photographers in Italy to reserve a section of his catalogues with photographs of costumes, which include isolated figures in the studio shots (street vendors, artisans, the carrier, etc.), genre scenes (the scribe, the thief, the beggar, etc.), street scenes, and photo montages (very famous one is the tarantella). In the nineties he took instantaneous photographs of street's scenes.