For what use?
I've created a custom Aperture metadata field "Comment" for in-house comments. In theory, this is never exported. Those who use it did not want it to be part of either the IPTC or the EXIF.
EXIF is supposed to be 'write once read many times' to record settings at the moment of capture. (Although some programs can edit EXIF data) You should use IPTC for this, which is the to record descriptions.
EXIF metadata is generally organized to reflect information about the digital image capture- information about the camera, settings, etc. EXIF was a standard created by an organization representing camera mfgs. The IPTC standard was defined by news agencies in the early 90s to record data about an image- photog, where, when, subject, + hundreds more. IPTC has been the generally accepted set of tags to use for data such as a comment.
You may want to take a look at this thread What is the best metadata field for picture TITLE?
In there there are links to the IPTC org site that gives suggested uses for the fields
So, in IPTC image description I would put something like Skiing in NH and in the IPTC caption field I would put "had a great day at Mt Snow with so and so .??
Unless you work for a press agency, you are free to use the fields however you wish.
IPTC stands for International Press Telecommunications Council. It's a consortium of news agencies.
Here is a guide to the use of IPTC metadata fields. Note that the specifications are in a rather constant state of flux. (Frank has pointed to other useful guides.)
If all you want is a text field to hold comments that are relevant to you, either borrow one of the IPTC fields, or just create a custom metadata field in Aperture. Either of these can be shown in a Metadata View and used when printing.
I keep titles of pictures in the IPTC "Title" field (I like to title prints for sale). If I have a description that I want to share with others, I put it in the IPTC "Caption" field. Comments that are meant not to be shared with clients I put in a custom Aperture field called "Comments" (e.g.: "Slightly OoF, but usable.").
As mentioned in this thread, it is not advised to store titles, captions, or comments in the EXIF.
As suggested by other replies, there are guidelines for what type of info goes in the different metadata tags. Being consistent, even to the point of keeping a log or journal, with the way you decide to add info is the key. Give some thought to how you have looked for pictures/images in the past and use those patterns to make the fields you use and the info in them a powerful cataloging tool. The camera will add date and time info. Newer ones add GPS data which is a huge time saver. Names, events, type of activity, other data that can either help find images in the future or can add info that won't otherwise be available 5 or 10 years from now. This can all be organized w/metadata and some planning.
Message was edited by: CDS1