Street photography has taken off, like a rocket, in popularity. Small mirrorless cameras like the Fuji X series, the Sony A7 and other compacts, that give photographers full manual control, not to mention amazing image quality, are the tools of choice. Images flood the internet on a daily basis, black and white images of popular neighborhoods and the interesting, or not so interesting, people of them are being added to photo sharing sites by the millions.
As of this writing it is not illegal to capture a photo of anyone in a public place and then display it for the world to see without any type of release. The guidelines of use for "Art" or "Editorial" images allow this in many locations throughout the world. First off, I am not a lawyer and this is by no means a guide to what the legal definition is but istockphoto.com defines it as follows
What you may not use these images for is, for instance, you photograph someone wearing a Tiffany watch and you want to sell the image to Tiffany to use in a national ad campaign. This use would not be allowed unless you had obtained a model release for the person you photographed or anyone else that is recognizable in the image that enhances the esthetic of that image. Any lawyers out there feel free to chime in.
The real question is what expectation do you have of privacy in a public place? If you have an emotional encounter with a loved one in a public space or you trip and fall and are embarrassed or you spill coffee in your lap. I could go on and on. All of these circumstances could be photographed by anyone within sight. These images could then be plastered all over the internet for the world to see. In this modern age this has become the reality.
As a photographer I believe I have a responsibility to act ethically and to work within the socially expected norms of where I am. I may not be bound by a written law that forbids me to take a photo but I must consider what the impact of that photo might be. Is it hurtful or could it incite violence? Could it embarrass someone or does it cross the line of being too intimate even though it is in a public space? These are all things that I personally must consider before taking an image. I have a social and professional responsibility when it comes to my photography. What I am most worried about is what would happen if photographers don't follow these types of guidelines. Society inevitably will fight back. Laws limiting, or eliminating photography in public spaces could occur. This article in Petapixel is an example of how this has already begun, "Arkansas Passes Privacy Bill That Could Kill Street Photography". This Bill was ultimately vetoed by the Governor when they realized the possible consequences. Then there is the opposite, the legislation know as the Ansel Adams Act which seems to be giving rights back to photographers. What is very clear is that this is just the beginning of this conversation.