A giant web of video-surveillance cameras has spread across Chicago, aiding police in the pursuit of criminals but raising fears that the City of Big Shoulders is becoming the City of Big Brother.

While many police forces are boosting video monitoring, video-surveillance experts believe Chicago has gone further than any other U.S. city in merging computer and video technology to police the streets. The networked system is also unusual because of its scope and the integration of nonpolice cameras.

The...