The verb фо́тать (some people perfer the variant фо́ткать) is a colloquial-speech substitute for long фоторгафи́ровать ‘to photograph, to take pictures’ (imperfective).
Нафо́тать = нафотографи́ровать — ‘to take a lot of picures’ (perfective).
Нафо́тай is the imperative.