Those small passport pictures are needed all the time. But unfortunately taking them is not that cheap normally.
At the moment Verkkokauppa.com has a really good offer though. Get six passport pictures for just 1.00 €. The offer is just valid Monday through Thursday from 9.00 till 16.00. You find the Verkkokauppa.com store at Länsisatama. You get there easily from the center by bus line 15 or tram line 9.