The center was created by the police commissioner, Raymond W. Kelly, as part of an effort to centralize the department’s information. The databases pull from 911 calls, arrests, complaints filed by victims, reports on accidents and moving violations. Detectives at the center mine these databases for nuggets of information that they send to officers on the street.

Image Videos detail birthmarks, scars, missing teeth and gold ones. The so-called blotchy database focuses on skin conditions. Credit... Chester Higgins Jr./The New York Times

To use the tattoo database, detectives can enter either words or images they believe may be in the tattoo. A search request can also include the part of the body that bears the tattoo.

The phrase “I love” comes back 596 times.

Dozens of people have “I love Mom” tattooed on their arms. One person has “Chi-Chi I love you.” Another has “Dollar Bills I love Money” tattooed on a hand. Then there is the New Yorker whose affection, perhaps for a former mayor, has been duly recorded: “I love Rudy.”

A search for the word “kill” in a tattoo produces 72 hits. Two people have the tattoos “Kill all rats.” Others say “ambition is a killer” and “kill cops.”

Investigators sometimes struggle to identify tattoos, said Sgt. Kevin C. Lonergan, who works at the crime center. “Jailhouse tattoos, tribal tattoos, those are sometimes hard to write down descriptions for because either we don’t know what they are or what they mean,” Sergeant Lonergan said. “Asian symbols are easier.”

The Police Department does not keep arrest reports when criminal cases have been dropped, said Paul. J. Browne, its chief spokesman. Nevertheless, the use of such databases has raised some questions about whether the department tracks too much information.

The New York Civil Liberties Union, for example, has criticized the department’s use of technology to collect data on people, regardless of their backgrounds. It has, for instance, questioned how the department handles images picked up by surveillance cameras and how that information is cataloged and stored.