Chapter 6: User Interfaces for Mobile Media 209 Even though we do not own the content, we can own the playlists and ratings that we give to songs. Some of the metacontent can originate from commercial or public services, such as the ID3 tags in MP3 fi les. Since digital content can be infi nitely reused, it encourages sampling – incorporation of pieces of music into new contexts. Currently popular tunes usually incorporate thousands of sound samples, many of them reused from other pieces of music. For instance, a kick drum sample in a typical drum-and-bass song may have been re-sampled by fi ve to ten different artists through as many successive generations of songs. Other examples of reuse are remixing, which involves taking pieces of music and rearranging and processing them in novel ways. This also includes mashups, which are created by taking two seemingly unrelated songs and joining them into interesting hybrids. Some artists are experimentally releasing their songs in multitrack formats that give users the freedom to remix the songs as they wish. In principle, this transfers some of the production responsibility from the producers to the consumers. While most people may still choose to enjoy music as it is, hundreds of thousands of others are increasingly treating music as digital objects that are just inviting to be modifi ed. 6.2.2 Photos Prior to the digital photo era, a photo was captured on fi lm by ex - posing it to light. The captured photo remained inside the camera until processed, in most cases in a commercial photo development lab. This was often done manually, allowing an experienced developer to signifi cantly enhance the technical quality of a photo. Each photo was valuable, since the fi lm could be exposed only once, and often the decision whether to take a photo or not was carefully considered. Once the photos were developed, they were sorted – failed shots were discarded, whereas the rest were stored, for example, in a shoebox stuck at the back of a cupboard, or in an album with dates and cap- tions. They were then later showed to relatives and visitors for their great pleasure, either by fl ipping through the album, or by browsing a pile of prints with the number of fi ngerprints showing an estimate of the viewing count. And now, photography is getting digital. In 2006, according to one study, some 70% of all photos were taken with a digital camera, while 4 it is estimated that the share will be 90% by 2010. This is a major 4 http://blogs.zdnet.com/ITFacts/?p=10613