There very definitely is imagery in "London" and I will briefly identify some of the most notable features for you. This poem presents us with the poet walking through the London streets near the River Thames. As he walks, he hears children and chimney sweeps crying, he sees blackened churches and hears whores cursing marriage. Everywhere there is evidence of suffering and unhappiness, creating a grim, dark and black mood.
However, one of the major pieces of imagery that is contained in this poem is "The mind-forged manacles" that the poet hears as he walks around. This is a very vibrant piece of imagery because it suggests that Blake feels the poverty and desperate situations that the people he sees are in are a result of other people's ideologies and thoughts. To a certain extent we are all the subjects of "manacles" forged by other minds or ideologies. Yet equally some have argued that this image refers to the manacles that we forge ourselves--perhaps Blake is pointing towards the way that we appear willingly to succumb to the restraints placed upon us and to become victims of our own exploitation.
In every cry of every Man,
In every Infants cry of fear,
In every voice: in every ban,
The mind-forg'd manacles I hear