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St. Mark's Square and the Rialto Bridge.

Iconic sights of Venice that attract thousands of tourists every day.

From a control room inside the city's police headquarters, they're being watched.

To combat over-tourism, officials are tracking every person.

Using CCTV, optical sensors and mobile phone SIM cards, they can tell residents from visitors, Italians from foreigners.

They know where people are coming from and where they are heading.

A month after cruise ships were banned from Venice, city authorities are preparing to ask visitors to pre-book.

And charge day-trippers between 3 and 10 euros to enter.

City Director General Marco Bettini says there's no alternative:

"I cannot guarantee a suitable visit to the city if we don't know how many people are coming to Venice and Venice, it's an island and is one of the cities that first, in the world I think, can prove that there is a physical limitation on the number of people that can be in the city at the same time."

Authorities have yet to decide how many people is too many.

The new rules are expected to come into force sometime between next summer and 2023.

Some Venetian businesses worry about the impact on their sales.

Tourists appear divided:

"I know so that there are some inhabitants of Venice who complain because there are too many people visiting the city but I think that the city lives also thanks to the tourists so maybe there are a little bit too many people sometimes but they should definitely find another way."

"I can understand it because the city is very overcrowded and it will probably be a lot nicer for the citizens of Venice."

One recent weekend, there were around 148,000 people in the historic centre of Venice.

That's before the full return of tourists from the U.S. and Asia.