I must admit that I go with Linda and find this project very interesting from an artistic perspective. For me this has much more layers than just the copying aspect, also it is about what is perceived as private (even if it is clearly not, if millions of people can watch it), or as art, and why, and so on. Still without a doubt I'd feel hurt and uncomfortable on a personal level if he'd used one of my pictures – and the fact that stuff like that is easily possible is actually one of the reasons that I rarely post a personal picture of myself, and would never, ever post pics of my children online.
I read through some of the comments on twitter and the articles posted here, and find it also fascinating that at least some of the people he used the pictures from didn't seem overly offended.
Natascha, I am not sure if it would also be possible to exhibit / produce these prints in Germany or Austria, which are countries with, as far as I know, stricter copyright laws, because 'artistic freedom' – I think, called 'fair use' in the USA – allows more than you may think. Still the outcome would probably depend on the specific case / lawyers / judges.
Apparently this artist has been sued several times with other projects, but always got away because of 'fair use'. And it's not only because the artist now is rich and can afford good lawyers, against the authors of the pictures, because apparently he won cases in the past against Marlboro, which also can afford very good lawyers, I presume.
As I said, I find it a rather intelligent, if disturbing project. Don't get me wrong, I don't 'like' like it, but I like that it makes me think. Which art, among other things, should do with people, in my opinion.
Maybe some of you may be interested in the approach on this student's work – it's his interface design bachelor thesis project:
http://interface.fh-potsdam.de/showcase/what/sousveillance/He printed out pictures he found on IG, hung them in the neighbourhood of the homes of the users (using their embedded geolocation information), took a pic of these prints which he again uploaded under a pseudo and tagged the original authors – getting the most different responses, from thankfulness to anger.