Unlike a normal camera, the iconograph contains a tiny imp who quickly paints the pictures (also called iconographs) of the subject at hand. If it is too dim for the imps to see, salamanders can be used as a flashgun.
CONNOR! (pimpernels!) here is a handy reading guide for discworld for you, to help clarify some things. the witches/tiffany aching series, DEATH novels, city watch, and moist von lipwig books (which now includes raising steam) are my faves and are most recommended. rincewind/the wizards are not very high in my estimation, but can be diverting. oh, and small gods can be life-changing, as several friends attest, particularly for those of a religious bent.