IPTC means International Press and Telecommunication Council and is a format used to store information in an image database. This includes information on image rights or names of photographers. It has been superseded by IPTC Core and now belongs to the XML metadata format XMP, which means Extensible Metadata Platform, created by Adobe.
With IPTC technology, you can store texts, keywords or copyright information directly in your own photos. Internet sites also take over these keywords, and if desired, they also appear in the web gallery or slide show. The IPTC standard also includes input fields for explanations that are stored in the image files. The IPTC information is part of the meta information that is used to describe images. Information on lens focal length or exposure time is part of the Exif information and also part of the meta data.
IPTC texts can be used in many ways. IPTC keywords are adopted as search terms by photo agencies and photo sharing sites on the Internet, which means that you no longer have to retype them online. For example, to use the keywords for the search query on your own PC, search for all photos that both contain the keywords "beach" and "sunset". Depending on the programme, image texts and headings from the IPTC fields appear in the slide show or web gallery.
The IPTC texts normally end up inside the image file. This is at least true for TIFF, PSD, JPEG and PDF. With raw files it is a bit more difficult. In many programmes, the raw formats of e.g. Nikon (NEF) or Canon (CR2) cannot be provided with IPTC information. This is only possible with your own camera programmes and costs extra. Photoshop saves IPTC texts in the secondary file of the image or in a central database, which loses the connection between the notes and the photo.
It is better to convert the raw file into Adobe's universal DNG format without loss. This also works with the free DNG converter. This generally also takes over IPTC information, even if this is not possible with all image programmes. In Adobe Lightroom, keywords are "stamped" into the images by mouse click. In Photoshop CS1 and the image database Bridge from version CS2, IPTC can be changed directly.
In the Photoshop versions, keywords and other IPTC information such as image texts, copyright notices and location information are saved. A single menu command writes the complete metadata set to all selected photos.