How do I use IPTC/EXIF metadata to categorise photos?

Question

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...

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"?

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".

So do the EXIF and/or IPTC standards allow addtional user-defined field names?

Thanks Kev

Answer 1

It can be used for that, but it really shouldn't: it's meant to be user-editable and so isn't a safe place to put critical metadata. Using an XMP sidecar is better for this kind of thing: in XMP, any field added that a given app does not understand is, according to the standard, supposed to be ignored by that app and not destroyed.

Answer 2

I don't know if there are applications to do this but by the standards described for JPEG files there is a field called Comments where you can assign values that could act like tags.

C# code:

using System.Windows.Media.Imaging;
using System.IO;

...

FileStream fs = new FileStream(@"<img_path>", FileMode.Open, FileAccess.ReadWrite);
BitmapMetadata bmd = (BitmapMetadata)BitmapFrame.Create(fs).Metadata;
bmd.Comment = "Some Comment Here";

also if you are looking for an application that already has this functionality built into it, then might i recommend Irfan View (open pic, go to Image menu, click on Comments button).

Hope this helps.