Virtual Graffiti consists of virtual objects and/or digital messages, images, multimedia or other annotations or graphics applied to public locations, landmarks or surfaces such as walls, train stations, bridges, etc. Virtual Graffiti applications utilize Virtual Reality and Ubiquitous Computing to anchor Virtual Graffiti to physical landmarks or objects in the real world. The virtual content is then viewable through devices such as personal computers, set-top boxes or mobile handsets, such as mobile phones or PDAs. The virtual world provides content, graphics, and applications to the user that are not available in the real world. Virtual Graffiti is a novel initiative aimed at delivering messaging and social multimedia content to mobile applications and devices based on the location, identity, and community of the participating entity.
This overall effort focuses on creating new mobile experiences based on merging virtual reality, Telepresence, and location based services. These experiences are seen to evolve over time based on the needs and capabilities of the users.
Location Based Messaging
This set of use cases is centered around a mobile user receiving or sending a message based on the computed location of the user. These include experiences such as
• A mobile user poses a query where the nearest Italian restaurant is and receives a set of messages and coupons from nearby restaurant proprietors.
• A user receives a message on her phone that there is an accident on the road a few miles ahead along with a suggested alternative route to take.
• Coworkers arrive in a conference room and receive a notification that the meeting has been moved to a new location.
These use cases are important because they serve as a basis from which the other use cases are built. The resolution of the messaging content is directly related to the accuracy with which the location can be computed.
Location Anchored Virtual Reality
This involves anchoring a virtual reality experience at a physical location. Thus the experiences in the virtual world can only be had at a specific real location. Several use cases that are included here are
• A virtual command post can be set up at the scene of an incident. This command post involves the sharing of information in the virtual world but can only be accessed by those at the scene of the incident.
• A set of blogs and media files are left at famous outdoor sculptures. Groups of friends can contribute, copy, and share files only while they are viewing the sculpture.
The phrase “virtual graffiti” has existed for a long time and has been applied to numerous different applications over the years. Originally, it referred to posting messages on electronic bulletin board systems and marking up whiteboard applications. From there, it developed in academia into contextual messaging applications. Several such examples are given below. In addition to contextual messaging, we also give some background information on three other key industry and entertainment applications.
Contextual messaging refers to leaving some type context-specific annotation, e.g. a virtual post-it note on a computer monitor, a time-sensitive message attached to a conference room telling the occupants you won’t be attending a meeting or location-based graffiti on a physical object.
Researchers at the University of Salford experimented with a CAVE system  in which a user could mark up a scene using 6-degree of freedom sensors. Obviously this is not something that is suitable for immediate use or mass market applications, but it serves as starting point from which other work could be derived.
Kit Hughes, during a research fellowship at the University of Georgia in 2003, developed a system in which users with WiFi-enabled mobile devices could mark up buildings in downtown Athens, Georgia with their own virtual graffiti via a process known as tagging  . In this system, the buildings are selected on a map and the graffiti is stored in a database where it can be accessed from other mobile devices and the project’s website.
A location-based messaging system  for leaving virtual post-it notes on physical objects was developed at the National University of Singapore. The system uses mobile devices as AR interfaces to view virtual messages associated with fiducial markers on physical objects.
In a project from Lancaster University  , mobile phones are used as digital spray cans. RFID tags are used to identify objects that can be marked up. The RFID tags can hold the identities of the last five people to leave graffiti. The graffiti itself is stored on a server indexed by RFID tag. When another user comes within range of an RFID-tagged object, the graffiti associated with that object is downloaded into their mobile device.
Social networking sites are proliferating across the Internet. These sites claim millions of user accounts from all over the world. The common thread between these sites is sharing. For example, people like to share photos via Facebook and Flikr, personal observations and rants via blogs on MySpace and Orkut, and even their knowledge via Wikipedia. Sharing can extend beyond the traditional definition of social networking to file sharing applications such as Napster, Kazaa, and Bit Torrent. Although the use of such applications for sharing copyrighted material is illegal, the cat has been let out of the bag, so to speak, and many users now demand the capability to share music, video, and data files. The rise of YouTube and its subsequent acquisition by Google despite its high-profile copyright infringement dramatically support this point.
Social networking is now going mobile through the development of Mobile Social Software (MoSoSo). Moblogging (mobile blogging) sites first rose in popularity in Japan but are now growing around the world. Mobile picture and file sharing are beginning to gain ground, as in Microsoft’s SLAM project (described in more detail later.) Some location-based mobile services now allow individuals within certain social networks to find each other when they are in close proximity and can even facilitate dating by ensuring that only those individuals who are known to someone you already know can contact you for such purposes (Dodgeball.com and Playtxt are two examples).
Gaming/entertainment applications can be divided into two categories: virtual and augmented reality environments. Classic examples of virtual reality applications include many of the massively multiplayer online role playing games (MMORPGs) such as EverQuest and World of Warcraft. These games are typically characterized by multiple players simultaneously logged in collaborating toward a shared goal but there are other virtual environments in which there is no shared goal or purpose. Examples of these include applications like SecondLife, the Sims Online, and CyWorld. These applications do offer other incentives, though, such as social interaction, creativity that can be expressed through custom content creation, and profitability via thriving online economies (EverQuest players sell virtual treasure collected during adventures on eBay; CyWorld users earn virtual currency by customizing their virtual rooms to entice others to visit them; Linden Lab’s SecondLife virtual currency can actually be exchanged for US dollars – the going exchange rate is about 250 to 1).
Teleconferencing involves face-to-face communication between remotely located individuals. Teleconferencing is currently experiencing a large-scale resurgence with product offerings from Cisco and HP for corporate applications, but it is also gaining traction on the smaller scale with application like Skype and iChat. It is not hard to imagine these video conferencing/face-to-face communication capabilities appearing on wireless devices in the future, extending current capabilities like push-to-talk group calls (iDEN) and push-to-view video calls (Samsung, LG). It is interesting to note that even though the term telepresence is used in relation to many of these systems, they do not embody anything more complex than basic video conferencing capabilities.
Virtual graffiti is also seeing use in the entertainment industry with a new attraction, the Virtual Graffiti Attraction. Using infrared spray cans and infrared webcam, projector and rear screens the guest can create "Real Life" graffiti on a virtual wall. The guest then receives the photo as a party favor. Some also say that this attraction could replace the photo booth that is now used at parties and carnivals.
- M. Y. Lim and R. Aylett (2004). "MY Virtual Graffiti System". IEEE Intl. Conf. on Multimedia and Expo, pp. 847-850.
- Kit Hughes. "EXPERIMENTAL WIRELESS ART PROJECT ENABLES VIRTUAL GRAFFITI". Retrieved 2003.
- S. Singh et al. (2004). "Augmented Reality Post-It System". ACM SIGCHI Intl. Conf. on Advances in Computer Entertainment Technology.
- P. Garner et al. (2006). "The Mobile Phone as Digital Spray Can". ACM SIGCHI Intl. Conf. on Advances in Computer Entertainment Technology.
- Air Graffiti Dallas: Virtual Wall 2013 http://www.airgraffitidallas.com