22 December 2010
Last updated at 12:40
The Izalco jail in Sonsonate, 60km from El Salvador's capital city, houses 838 inmates. All are members of one of the country's violent street gangs known as the 18.
Gangs like the 18 took shape in the US in the 1980s. Nearly a million Salvadorans fled the civil war, many of them settling in Los Angeles where gang violence was rife.
In the 1990s, the gangs or "maras" spread to Central America after many of their leaders were deported from the US. Several thousand gang members are in El Salvador's jails, about a third of the prison population.
Many of the inmates have tattoos that identify them as 18 members. This trend is said to have faded in recent years amid moves, the most recent a law passed in September, to criminalise belonging to a gang.
The army is in charge of security at El Salvador's prisons. Visitors are strip-searched and have X-ray scans to try to prevent them from smuggling SIM telephone cards for inmates.
But prisoners find ways to get around regulations. Here an inmate in solitary confinement (top photo) uses a tiny mirror to communicate with other prisoners, while on the right a prisoner hands over an object using a string.
Inmates are responsible for distributing food and cleaning the jail. The Izalco prison is being expanded to be able to hold nearly 3,000 prisoners.
But with inmates living in frequently cramped conditions, tempers often flare and riots are common in El Salvador's jails.