Graffiti doesn’t have to be a criminal offense. As part of its Street Summer season, Channel 4 has unveiled an iPhone app called Street Tag that allows users to virtually graffiti the streets. Using augmented reality technology, the app transforms phones into virtual spray cans. Wannabe street-artists can paint any surface using their iPhone and the results appear in real time through the phone’s interface. Once the tagging is finished, it can be geo-tagged and shared via Facebook, Twitter and email. The app launch coincides with a programme of events and contests celebrating urban, street-art and hip-hop culture in Channel 4’s Street Summer series. Augmented reality technology is creating a giant virtual layer of information around us to help enhance our experience of the real world. And now brands are using it too. For instance, beer brand Beck's is using it for its Green Box Project, which enables people to reveal invisible artwork using their mobile phone.   We look forward to seeing more of these virtual campaigns, and exploring our environment in a completely different way.