。
Lots of pictures are hanging on the wall.
Literal
Wall [on-に] lots-of paintings [subject-が] hanging are.
たくさんの絵 is 'lots of pictures' — たくさん as a quantifier modifying a noun via の. かかっている marks the resulting state of being hung. A basic existential pattern: location-に + subject-が + state. The unspecified plural たくさん is the natural way to indicate a large but uncounted number.