What are the strong images in the poem "London" by William Blake?

There are three strong images in "London." All of them are nearly surrealistic, like scenes painted by Salvador Dali.

How the Chimney-sweeper's cryEvery black'ning church appals

Chimney-sweepers were small children. They had to be small in order to be lowered down through chimneys in order to sweep off the accumulated soot. It was a terrible profession for children because breathing all that soot led to early deaths from lung disease. The churches in the...

There are three strong images in "London." All of them are nearly surrealistic, like scenes painted by Salvador Dali.

How the Chimney-sweeper's cry
Every black'ning church appals

Chimney-sweepers were small children. They had to be small in order to be lowered down through chimneys in order to sweep off the accumulated soot. It was a terrible profession for children because breathing all that soot led to early deaths from lung disease. The churches in the image appear to be blackened by the soot of the chimneys because the clergy does nothing to help the children who are enslaved by brutal employers and doomed to die.

And the hapless Soldier's sigh
Runs in blood down Palace walls.

Blake is referring to the plight of veterans who have been maimed in battles. They are destitute because they receive no pensions from an ungrateful government. Surrealistically, the sighs are turned into blood which runs down the walls of the royal palace where the aristocrats inside are indifferent to the despair of the veterans.

But the most striking image of all is the last one:

But most thro’ midnight streets I hear
How the youthful Harlot’s curse
Blasts the new born Infant’s tear,
And blights with plagues the Marriage hearse.

Very young girls were forced into prostitution because of poverty. It is bad enough to see them soliciting in the streets, but it is worse to hear girls who are still children learning to curse like hardened prostitutes. These girls are nearly certain to contract a venereal disease and to pass it on to their customers. If a man with syphilis gets married to a healthy young woman, he will pass the disease along to her, and then when she has a baby, her baby will inherit the disease from its mother. That is what Blake means by "Blasts the new born Infant's tear, and blights with plagues the marriage hearse." The infant is born with its body already infected, and the Marriage hearses often transport new brides to honeymoon havens where they are destined to become infected by their husbands (men who were infected by the "youthful harlots").

In each of the three images, a sound is translated into a visual image. A chimney-sweeper's cry becomes a soot-blackened church wall. A soldier's sign becomes blood running down the stone walls of a palace. A child-prostitute's curse becomes a disease-riddled infant and a germ-infested wedding carriage.