How much ownership do we have over a Tweet once its published for the world to see online? Where is the line between private and public? In Brazil, where racism is a national issue, ‘virtual racists’ are being shamed on billboards in their neighbourhoods.

Public shaming is back on the agenda. From fears of being photographed eating on the tube, to apps that erase pics from the night before – the spectre of public criticism looms large. Has social media revived this age-old mechanism of control? Or can shame be a force for positive change?

Whether you're a woman eating on the Tube, or a sleeping commuter, the combination of social media and smartphones mean that no public space is safe to do anything you wouldn't want caught on camera. Is it just a bit of harmless fun, or something a little more sinister?

As young Australians head for bright city lights, Melbourne has become the nation's fastest growing area. But how do their parents get them to visit home out in the sticks? A campaign by Victoria’s public transport operator V/Line let people guilt trip their kids into returning.