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"They're impacted by every decision we make, but they're powerless. If anyone has the right to spy on us, it's our descendants."

He describes what he is doing as, effectively, "surveillance"-intentionally using the "highly loaded" word.

But his aim is to provoke discussion, especially following the uproar caused by recent revelations of mass US spying.

"This surveillance is completely out in the open, and that encourages the conversation about surveillance to be completely out in the open, as it needs to be."

"Nothing is hidden here, except for the cameras themselves."

So how will the 100-year photographs work?

With simplicity and, of course, durability uppermost in mind, Keats' steel canister cameras use black paper, instead of photographic paper, that will fade with the highly focused and very low light trained through the pinhole.

"If you have a camera directed toward some houses and those houses get bulldozed after 25 years and they build a skyscraper, what you'll see are just the ghosts of the houses, a shadow of the houses.

"The skyscraper will be bolder in the same image. It'll be a double exposure in effect," he says.

Dressed in an every man sweater and jeans, the bespectacled Keats, whose past projects include ballet for honeybees and a travel documentary watched by plants, admits there is plenty that could go wrong.

"First of all, the technology hasn't been tried and as a result we are working based on some assumptions," he says.

But plans are already afoot to organize the project in other cities and Keats even hopes the United Nations could get involved.

The challenge for those hiding the cameras is to choose a spot worthy of century-long observation, says Julia Schulz, of Team Titanic.

"It'll be interesting to see if people choose a well-known place such as the Berlin Wall - or their own little plot of garden."