Describe the manner in which data elements are linked across databases.

Almost every city street in London is under constant video surveillance, partly as a reaction to terrorist attacks. These closed-circuit cameras initially created tapes that could be viewed later, but the technology now is far more capable. The cameras, now also mounted in police vehicles, are equipped with automatic number plate recognition (ANPR) capabilities, which use optical character recognition to decipher the license plate numbers and letters in near real time.