The foaf:depiction property is a relationship between a thing and an
foaf:Image that depicts it. As such it is an inverse of the
foaf:depicts relationship.
A common use of foaf:depiction (and foaf:depicts) is to indicate
the contents of a digital image, for example the people or objects represented in an
online photo gallery.
Extensions to this basic idea include 'Co-Depiction' (social networks as evidenced in photos), as well as richer photo metadata through the mechanism of using SVG paths to indicate the regions of an image which depict some particular thing. See 'Annotating Images With SVG' for tools and details.
The basic notion of 'depiction' could also be extended to deal with multimedia content (video clips, audio), or refined to deal with corner cases, such as pictures of pictures etc.
The foaf:depiction property is a super-property of the more specific property
foaf:img, which is used more sparingly. You stand in a
foaf:depiction relation to any foaf:Image that depicts
you, whereas foaf:img is typically used to indicate a few images that are
particularly representative.