“When I first noticed this scene in Birkenhead, I was immediately taken by the metaphorical image of a person trapped or imprisoned behind the wall. Although the building pictured is not used for incarceration, the harshness of the composition and the expression of the figure made me immediately think of prison or confinement. It seems to sit well with statistics about crime and punishment in unequal societies.” The proportion of the population imprisoned in a society is influenced by four things: crime rates, conviction rates, the tendency to give prison sentences rather than fines or community service and the lengths of prison sentences.

Some societies use imprisonment far less, and when they do imprison people, they put more emphasis on training and rehabilitation so that re-offending rates are also lower. In the UK, despite falling crime rates, imprisonment rates have been climbing steadily for decades leading to a crisis of prison overcrowding. In the USA only about 12% of the growth in prison populations is due to an increase in crime. In both countries the rise in prison populations over recent decades seems to be primarily the result of more punitive sentencing. In a study published in the journal Social Science and Medicine, strong links were found between imprisonment and income inequality – both internationally and among the 50 US states.