88 Personal Content Experience: Managing Digital Life in the Mobile Age Besides at the point of creation, automatic metadata can also be added at a later stage. It may be based on mechanisms that fi rst rec- ognize some specifi c features from the content, and then translate them to metadata symbols. It is feasible to develop systems that can accurately count the number of people in a photo, but identifying whether one of them is Michael Jackson is more diffi cult. The challenge of such automatically entered metadata is that it (currently) captures characteristics that are technical and therefore irrelevant to most users. Of course it may be possible to derive further information based on automatic metadata; a simple example is that date of creation implies the season, or that the use of a fl ash can imply dark conditions. However, deriving such metadata is still largely experi- mental, and requires advances in pattern recognition, context aware- ness, and artifi cial intelligence in general. We will discuss the potential of deriving metadata in section 4.4. As with any automation, the major pitfall of using metadata to auto- mate operations is that if the criteria for the operations are not clearly visible, the resulting view may be diffi cult for the user to comprehend – especially if the criteria involve multiple attributes that are not all visible. As a result, the users become frustrated as they cannot locate a certain item, or the grouping of the items is not obvious. The history of an object can provide new metadata. It can be useful to track the user’s interaction with the object and attach that informa- tion incrementally based on the various moments in the object’s life- cycle (Figure 4-4). In this way the system can identify what objects are used often, which in turn indicates their value and importance to the user. In addition to time and date, the interaction metadata attributes can describe the action (such as open, edit, send) and parameters (such as to which telephone number the image has been sent). Note that such metadata creation takes place after the content object itself has been created. There are networked services that provide metadata related to the content object automatically. Today, this is routinely done in the music management software for MP3 players. The metadata in the fi les typi- 21 cally comes from Internet services, such as freeDB. CD ripping soft- ware acquires the metadata from the services and inserts it into the ID3 attributes of the MP3 fi les. As soon as one user has fi lled in the metadata for a new CD, it becomes available for other users of the same CD. 21 http://www.freedb.org/