IPTC data is a method of storing textual information in images defined by the International Press Telecommunications Council. It was developed for press photographers who need to attach information to images when they are submitting them electronically but it is useful for all photographers. It provides a standard way of storing information such as keywords, location and captions.
Because the information is stored in the image in a standard way this information can be accessed by other IPTC aware applications and the images become "searchable" by Windows Explorer (Windows) or Spotlight (Mac) no matter where they are stored in the hard drive. As photo or image tagging is both time consuming and labor intensive when the volume is large, outsourcing of this kind of job is cost effective.