U.S. Immigration and Customs Enforcement officials nabbed Letha Mae Montemayor, 52, outside an apartment complex about 7:30 p.m. after receiving five separate tips from the public.
"This arrest would not have happened without the public's help, and it demonstrates how much individual citizens can do to help law enforcement attack crime," ICE Director John Morton said in a statement.
"The best way to protect innocent children from sex offenders is for law enforcement, educators, parents and concerned citizens to join forces
Montemayor is believed to be the woman who appears along with a still unidentified man in child pornography dubbed the "Jen Series," which federal officials discovered in Chicago in 2007.
It has since been recovered in the collections of about 275 other child pornography suspects across the country.
The break in the case came after U.S. Attorney Andre Birotte, Jr., and other federal authorities released photos of both suspects to the media at 10:30 a.m. Thursday.
They received their first tip about 2 p.m.
Claude Arnold, ICE special agent in charge of homeland security investigations in Los Angeles, said once authorities learned the woman's name, they pulled her photos from public databases and noted similarities to the images that appeared in the Jen Series.
Arnold said federal authorities and officers of the Los Angeles Police Department then placed Montemayor under surveillance and arrested her at 7:30 p.m. without incident on a federal charge of producing child pornography.
Montemayor was identified both through her facial appearance and tattoos - a black butterfly on her right hip, a curled up cat on her right shoulder, writing on her
"This significant development brings us one step closer to vindicating the victim and helping to regain some dignity for all victims of child exploitation crimes," Birotte said.
Arnold declined to provide Montemayor's address, nor any details about whether she has a criminal record, or lives or works with children.
He did say there were no children in her apartment at the time of her arrest.
Montemayor is in the custody of the U.S. Marshals Service, undergoing questioning. Arnold said she may appear in federal court Friday or Monday.
The man who appears in the Jen Series remains at large, and the investigation is continuing. The identity of the victim also remains unknown.
"We're still seeking the public's help," Arnold said. "Anyone who can give us information, including the victim herself, should come forward and help us to also identify and apprehend John Doe so we can prevent other children from being victimized."
The Jen Series consists of about 40 photos probably taken 2001 at an apartment in the San Fernando Valley, likely in Encino - based on a calendar from a local business, a Yellow Pages phonebook and cable box that appear in the photos.
The images show a girl, then between 11 and 14 years old, being abused by a woman now believed to be Montemayor, as well as a Caucasian man in his 40's or 50's.
A digitally-applied black dot covers most of the man's face, but he appeared to have brown or gray straight hair, and graying facial hair, in the photos. He also had a distinctive pair of moles about an inch apart, one on top of the other, on the center of his chest.
The "wanted poster" can be seen on www.ice.gov.Anyone with information that can assist in the investigation is urged to call 1-866-DHS-2ICE.
Montemayor is the 246th suspect swept up by ICE Homeland Security Investigation's Operation Sunflower.
The international operation rescued 123 victims of child sexual exploitation, including 44 who were directly rescued from their abusers.
The children included five toddlers under age 3, 41 who are grade school age, and 53 teenagers. There were also 24 adults who had been victimized in their youth.
Operation Sunflower has concluded, but similar efforts are continuing under Operation Predator.