title: How do I use IPTC/EXIF metadata to categorise photos?
body: <p>Many photo viewing and editing applications allow you to examine and change EXIF and IPTC data in JPEG and other image files.  For example, I can see things like shutter speed, aperture and orientation in the picture files that come off my Canon A430.  There are many, many name/value pairs in all this metadata.  But...</p>
  
  <p>What do I do if I want to store some data that doesn't have a build-in field name.  Let's say I'm photographing an athletics competition and I want to tag every photo with the competitor's bib number.  Can I create a "bib_number" field and assign it a values of "0001", "5478", "8124" etc, and then search for all photos with bib_number="5478"?</p>
  
  <p>I've spent a few hours searching and the best I can come up with is to put this custom information in the "keywords" field but this isn't quite what I'm after.  With this socution I'd have to craft a query like "keywords contains bib_number_5478" whereas what I want it "bib_number is 5478".</p>
  
  <p>So do the EXIF and/or IPTC standards allow addtional user-defined field names?</p>
  
  <p>Thanks
  Kev</p>