With Snapchat and Instagram it is all too easy to abuse picture taking and really inexpensive to snap a photo of an unknowing stranger. If you are in public and will only post pictures online without their permission, can the victim take legal action against you?
What would be the effect on the photo taker? Will there be punishment for the host company (if it encourages this type of behavior)?
In the United States, You have no expectation of privacy in public. Anything you can see from a public place, you can take a picture of, even if the "victim" is in their own home but has the blinds open. If you are standing on a public sidewalk or street, you would legally be able to take a picture with certain exceptions.
An exception to this would be: if with just your eyes you can see into a private home, you can take a picture of that, but if you require a telescopic lense with some sort of IR adapter to "see through" blinds. That MAY be considered illegal.
For real world examples of this question, check out PINAC.
Another example is "Creepy Camara Guy", https://www.youtube.com/watch?v=vs6iLtl0BAw. This guy basically goes around recording videos of people in public in a VERY obnoxious way. But he is within his legal right. (Note: Video unavailable: "This video is no longer available because the YouTube account associated with this video has been terminated.")
Taking the picture is one thing. There are also laws about what you can do with it: In the United States you cannot in general use a person's image for "commercial purposes" without their permission, but you can use it for "editorial purposes." The line between the two purposes can be very tricky, and is tied to the "Right of Publicity." Which is why you will often see some peoples' faces obscured on reality TV: those are people from whom the producers couldn't get a release, and thought it not worth risking a "commercial use" claim.
For other jurisdictions, Wikimedia Commons has a list of countries and what you are allowed to do with pictures taken in public.
https://commons.wikimedia.org/wiki/Commons:Photographs_of_identifiable_people
To get details, click one of the country names and you will be taken a page which provides legal references for most countries.
For the point of view from another jurisdiction (Australia) see How do laws affect photography of non-humans in public when people may be in the frame?
To repeat:
In R v Sotheren (2001) NSWSC 204 Justice Dowd said “A person, in our society, does not have a right not to be photographed.”
In general, you can take photos of people when you are on public property or private property (which includes inclosed public land e.g. public schools) where you have permission to be (and to photograph from). You can photograph into private property using any technology legally available.
There are limitations mainly related to voyeurism and commercial use, which are discussed at http://www.4020.net.
