The American Civil Liberties Union of Illinois called for a full review of the system - with at least 10,000 cameras mounted at locations from skyscrapers to utility poles - saying city officials won't release basic information such as the exact number and cost of the cameras, nor any incidents of misuse.
Those concerns, along with city officials' plans for expansion, put Chicago a step closer to a Big Brother invasion of privacy, the ACLU said.
"Chicago's camera network invades the freedom to be anonymous in public places, a key aspect of the fundamental American right to be left alone," according to the report released Tuesday. "Each of us then will wonder whether the government is watching and recording us when we walk into a psychiatrist's office, a reproductive health care center, a political meeting, a theater performance, or a book store."
The system, which started less than a decade ago, was called the most extensive and integrated camera network of any U.S. city by former Homeland Security Secretary Michael Chertoff.
Chicago police have praised the cameras' use, and Mayor Richard Daley has even called for cameras to be installed on every city corner to help fight crime. Police and Daley have said the cameras help authorities respond more quickly and have led to more than 4,000 arrests.
City officials responded later Tuesday to the ACLU's report, saying the cameras help police, are used in a public way and are monitored.
"The cameras supplement the work of police personnel in the field, and save local taxpayers money by freeing up police resources to protect other areas not covered by surveillance cameras," Jose Santiago, executive director of Chicago's Office of Emergency Management and Communications, said in a statement.
Santiago said that since 2006, the cameras have been used to help solve more than 4,500 crimes and "prevented an untold number of crimes." There are safeguards in place to prevent abuse, he said, noting that all images are erased after two years.
The network includes private cameras and those installed by city agencies, such as the Chicago Transit Authority. While many of the cameras are visible - like those with flashing blue lights affixed to street poles - countless others are unmarked. City officials have been tight-lipped about how many cameras Chicago has in place, but no one disputes that there are at least 10,000, including more than 4,000 installed by Chicago Public Schools and at least 1,000 at O'Hare International Airport.
In its report, the ACLU outlined three specific technologies that exceed the powers of ordinary human observation and increase the government's power to watch the public: zoom, facial recognition capacity and automatic tracking.
Santiago said Tuesday that the cameras don't have all those technologies.
"Chicago's growing camera network is part of an expanding culture of surveillance in America. Combined with other government surveillance technologies, cameras can turn our lives into open books for government scrutiny," the report said. "Chicago's camera network chills and deters lawful expressive activities protected by the First Amendment, like attending a political demonstration in the public way."
ACLU officials said the city declined to give the group information on the cameras, including a tour of its operation center, statistics on crime and cost estimates. According to the report, surrounding communities have paid hefty sums for cameras; suburban Cicero has 30 cameras which cost $580,000.
The group said that money could be better spent, for example by putting more police officers on Chicago's streets. It added that there has been little research to prove that the cameras deter crime.
In addition to the moratorium, the ACLU recommended more public input, regular audits, rules and regulation on who can view the images, public notice before installing a camera and disclosure of any abuse. The report cites cases in other cities where "male camera operators have ogled women."
Public complaints about the cameras haven't been widespread and are generally limited to those who get caught for a minor offense or if the cameras fail to record a violent attack.
Authorities have said the cameras played a prominent role in solving several high-profile cases. Footage from a city bus camera helped persuade a suspected gang member to plead guilty to shooting a 16-year-old high school student in 2007. Cameras helped police determine that the 2009 death of a school board president was a suicide.
Chicago police spokeswoman Lt. Maureen Biggane said she had not seen the ACLU report.
"The Chicago Police Department is committed to safeguarding the civil liberties of city residents and visitors alike," she said in a statement. "Public safety is a responsibility of paramount importance and we are fully committed to protecting the public from crime, and upholding the constitutional rights of all."