Facial detection technology in the new Piccadilly Circus lights in London is "incredibly intrusive", according to privacy campaigners.
The revamped screen in the British capital will be turned on later in October in a space where 100 million people pass each month.
Cameras hidden in the screen will detect people's faces, figuring out their age, gender and mood, and use that to tailor brand messages.
According to Ocean Outlook, the company that provides the screen's technology, the system can detect people's age and gender with 90% accuracy.
The system can identify the makes of vehicles and will also feature wi-fi to let people interact with the screen, but also potentially to track mobile devices.
Privacy campaigners say signs should be put up to inform the public they are being monitored.
Renate Samson, chief executive of Big Brother Watch, said: "From a privacy and security point of view, we think (it) is incredibly intrusive.
"It literally is Minority Report."
Landsec, the company which owns the screen, said in a statement: "Although the Piccadilly Lights screen will be able to display advertising content that responds to real-time factors - such as the weather or the colour of cars - the technology is not able to recognise individual people, or display individually targeted content.
"The screen does not collect or store personal details or data."
The famous billboards have been out of action for nine months while a new, 790-square-metre screen has been fitted.