Metadata Concepts
Several types of metadata can be stored in an image file, and each type can serve a different purpose. One type, technical metadata, is used to describe an image in a technical sense. For example, technical metadata can include attributes about an image, such as its height and width, in pixels, or the type of compression used to store it. Another type, content metadata, can further describe the content of an image, the name of the photographer, and the date and time when a photograph was taken.
Metadata is stored in image files using a variety of mechanisms. Digital cameras and scanners automatically insert metadata into the images they create. Digital photograph processing applications like Adobe Photoshop allow users to add or edit metadata to be stored with the image. Annotating digital images with additional metadata is a common practice in photographic and newsgathering applications and for image archiving usages, as well as at the consumer level.
Storing metadata together with image data in the same containing file provides encapsulation. With encapsulation, both types of data can be shared and exchanged reliably as one unit. Metadata that is stored in the image file format is referred to as embedded metadata.