This is what I'm thinking too. Cool idea and pics and he has good intentions, but I don't think it's right to take pics of people and post them online without their knowledge and permission. It's very presumptious of the photographer. If I saw someone taking my pic on the train I'd freak out!
As a New Yorker who often practices what is called 'street photography', which this essentially is, the law on this is very clear. An artist has a right to take a photograph of anyone in a public place at any time and for any reason, without permission. That includes children, women, the homeless, police, firemen, and so on and so forth. The artist also has the right to exhibit this work on the internet and/or in an art gallery without a model release.
The artist does not have the right to use the work for commercial purposes. For example, they cannot use a photo of a woman reading 'Fifty Shades' on the back of the book or in an ad suggesting you buy the book without a model release but they can use the image as art in a gallery like the one this guy is doing.
An artist can take photos of private property including your house, landmarks, bridges, infrastructure, and so on, provided he is standing on public property while doing so.
(All this assumes there is not a local statute overriding this which there is not in NYC).
A photographer does not have the right to take any photos whatsoever on private property without the permission of the property owner. Nor does a photographer have a right to take a picture where you have a reasonable expectation of privacy, such as in a dressing room, bathroom, or other private areas.
Anyone who complains about being photographed in NYC these days is pretty funny. When you are walking down any street in the business districts, you are being filmed by high resolution video cameras owned by private property owners, the NYPD, and the Department of Homeland Security. Often the bored security guards that operate these cameras, especially the private ones, will entertain themselves by people-watching.
There's a lot of attitude in NYC by people who claim they know this or that about photography and privacy, but it's just attitude and not knowledge.
If taking photos on the streets of New York was illegal, Robert Frank, Garry Winogrand, Lee Friedlander, Henri Cartier-Bresson, William Klein, and so many other great photogs whose work sells for tens of thousands of dollars, would have been in jail.