They steal into desolate spots of the city, or, if they're feeling brazen, roll up to well-traveled street corners, bearing bags of trash, old mattresses, and tires.
The city spends $1.5 million or more each year cleaning up the junk they leave behind - including 100,000 tires - only to watch it pile up again.
The results for Philadelphia: health and fire hazards and nicknames like "Filthadelphia."
The perpetrators have always been elusive to police and even block captains, but no more. Strategically placed crime cameras are catching them in the act.
Since last year, the city has employed hidden cameras at sites popular for "short dumping," so named for the trash that lands short of its proper destination.
The cameras have helped the city ticket 71 people for the crime since early 2010.
It's not a big number, but city officials say the cameras are curbing the problem, though community-led cleanups and a public education campaign also have helped.
The Streets Department cleared 16,590 tons of garbage from 1,047 illegal dumping locations for the year that ended June 30, down from 17,682 tons from 1,368 spots the previous year.
The city is seeking a federal grant to buy 25 more cameras for about $5,500 each.
Despite the efforts, some neighborhoods are still overflowing with trash. And the images captured by the hidden cameras reveal why.
The incriminating photographs show dumpers nonchalantly unloading trash bags from their cars or trucks and pitching them onto the street.
It's not just an urban problem. A survey released last month by the advocacy group Keep America Beautiful found 123 illegal dumping sites in Bucks County with an estimated 223 tons of trash.
Many who dump in Philadelphia don't live in the city, officials said, and some are ditching construction detritus and don't want to pay to get rid of it.
But the motivation for many violators, who toss bags of trash that they could easily put out on the street for pickup, remains a puzzle.
"I think it's just their careless attitude toward the city, and maybe toward themselves," said Tom Conway, the city deputy managing director who oversees the camera program.
Conway speculates that many of the dumpers cleaned out apartments for a move, were not going to be around for trash day, and took the trash to a remote location.
Michael Quintero Moore, who spends a good part of his work life solving short-dumping problems in City Councilwoman Donna Reed Miller's Eighth District, which stretches from North Philadelphia to Chestnut Hill, has a simpler explanation.
"Some people are just trifling," he said. "It means people are just lazy."
Conway's office gets license-plate numbers from the photographs and turns the information over to the police Neighborhood Services Unit, which tracks the offenders down and issues tickets. Fines start at $300.
Since 2009, the police Neighborhood Services Unit, which also does live surveillance in problem areas, has arrested 83 people for illegally dumping trash.
"We've seen everything - refrigerators, horse manure, branches, and trees that people could just throw back into the forest," said Ricky Whitfield, an officer in the unit. "But our worst thing is the tires. They'll dump them on the railroad tracks. They'll dump them anywhere they can."
That can create real dangers. In 1996, teenagers set a mound of tires under I-95 on fire, severing the expressway and snarling traffic.
"It's overwhelming, especially with four officers doing the whole city," Whitfield said. "But we put a dent in it."
On July 16, the city introduced yet another strategy - a program that pays registered neighborhood groups 50 cents for each tire they turn in, prompting people to drag in 8,882 tires so far.
Tracey Gordon, a block captain in West Philadelphia and a frequent critic of the city's slow response to reports of short-dumping, said the cameras and related programs are helping.
"I see that they're trying," said Gordon, who ran unsuccessfully for City Council in the May primary. In fact, she says she would like a camera for trouble spots in her neighborhood.
There is no excuse for people to dump their trash illegally. People can take as much as a carful of garbage to three dumps that the city runs. For locations, go to: http://www.phila.gov/streets/Sanitation_Convenien.html.
For larger loads, Home Depot sells the "Bagster," which holds 3,300 pounds of junk and costs $150 to have hauled away.
Carlton Williams, deputy commissioner for the Streets Department, said the city's efforts to clean up sometimes seem to encourage the problem. Near Malcolm X Park in West Philadelphia, neighbors keep tossing trash 52d Street and Larchwood Avenue.
He says people put the trash at the corner partly because they know the Streets Department has cleaned up there.
"It's definitely a frustrating situation," Williams said.
The dumpers also have figured out that the city goes through the trash to find bills or other identifying information. More and more often, paper with addresses is taken out of the garbage, making the offenders hard to catch, Williams said.
The cameras, police officers, and Streets Department employees can't be everywhere. Enforcement can even produce additional victims.
Che Rose, who runs Che Bar & Grill in West Oak Lane, has watched a mound of trash grow behind her bar for three years.
"There's everything in there," she said, staring at the junk piled behind her bar. "Bags of grass and leaves, tires, everything."
She says she doesn't know who dumped the trash, which includes a decaying box spring and a couch. It is not even on her property, but it is behind her restaurant, causing the city to cite her - wrongly - several times.
After calling Miller's office, Moore helped Rose prove that the property belongs to a nearby apartment building.
The city plans to clean the garbage up and bill the apartment building.
Rose hopes that will happen in time for the Aug. 20 Stenton Avenue Community Festival she organizes. Short-dumpers are not invited.
See a video about the city's efforts to stop illegal dumping at www.philly.com/dumping