Chapter 4: Metadata Magic 97 holiday trip) or place (such as home or a theme park), which are dif- fi cult for the device to know even though they may be obvious to the user. The temporal dimension is perhaps the easiest to take into account in organizing an object; just study the deviation of capture times of the images. Some other aspects would benefi t from using location information or discovering other devices nearby. 4.5.4 Automatic Summarizing Automatic summarization of content is related to grouping, but its aim is different as it goes one step further. As grouping is targeted at creat- ing collections of objects that share similar characteristics, summariza- tion is about fi nding, for instance, the most representative or novel object from the collection, or condensing a set of objects into a single summary object. Consider image grouping. Automatic summarization selects an image that presents the group in the best way. The result can provide unexpected and fresh views to existing content – or sometimes fail completely, as is normal for automatics that operate outside the expected conditions. One use for auto-summarization is storytelling: sharing personal experiences by generating an instant story based on a large set of objects. For instance, instead of going through the gallery of your holiday trip and wondering what to show, the system can generate a story based on the time, the travel route, and the captured content. The result may not be perfect but still suffi cient to keep your politely interested dinner guests from falling asleep in the middle of your slide show. 4.5.5 Enhancing Privacy and Security As mobile devices are becoming more vulnerable to different kinds of threats (such as viruses and malicious software), fi nding new ways to enhance security is increasingly important. Metadata can be used towards this aim by preventing the execution of some operations auto- matically, or blocking content that does not contain a certain combina- tion of metadata attributes and values. Furthermore, the system could use a third party to check the metadata and determine whether the content can be trusted or not. Of course, also the metadata is itself content that needs to be protected. User privacy can be enhanced by excluding private data from sharing or publishing on the basis of metadata. For example, a privacy rule might dictate that if the metadata contains the name of the