Examples of metadata are the tags you assign to a bookmark saved on the del.icio.us site or the tags you add to a picture you store on a photo sharing site like flickr. They are added on to allow subsequent retrieval and analysis.
Some metadata is generated automatically. For example, digital cameras add metadata to every image you capture. The data is recorded in a standard format called EXIF, the exchangeable image file format. EXIF metadata includes the following:
In the future, we can expect to see this extended to include the location (latitude and longitude) at which the picture was taken, and perhaps even the direction in which the camera was pointed. The location will be recorded automatically, because cell phones and digital cameras will include GPS (global positioning system) chips which are now under $5 from manufacturers.