XMP

Extensible Metadata Platform (XMP) is a metadata standard that can be used with a variety of file formats. When stored in a file, it is usually represented in a text format based on XML.

Related formats
The XMP Specification (Part 3) defines how to embed XMP in some popular file formats:
 * In a TIFF file, tag 700 is used.
 * In a JPEG file, an APP1 segment with identifier "http://ns.adobe.com/xap/1.0/" is used. Sometimes there are also APP1 segments with identifier "http://ns.adobe.com/xmp/extension/".
 * In a PNG file, an iTXt chunk with keyword "XML:com.adobe.xmp" is used.
 * In a JPEG 2000 file, XMP is stored in a "uuid" box with a particular ID. Apparently, it may also be stored in an "xml " box.

Other related formats:
 * IPTC Photo Metadata

Specifications

 * XMP Specification Part 1: Data model, serialization, and core properties
 * ISO 16684-1:2012
 * XMP Specification Part 2: Additional properties
 * XMP Specification Part 3: Storage in files