Metadata
Information stored within or alongside an image file that describes the picture rather than forming part of it.
In depth
Metadata falls into three families: technical data written by the camera, descriptive data added by the photographer, and administrative data covering rights and contact details. It is what makes a large archive searchable, and stripping it — as many social platforms do on upload — severs an image from its authorship.
Examples in practice
Searching an archive for frames shot at over 200 mm at ISO 1600 in a given month relies entirely on metadata.