Custom descriptors vs EXIF vs IPTC

Question

I'm planning to create a digital archive of family photos which will include data on family name, description of the scene in each photo, etc. I'd like the data to be stored with the photo and readable by other software. So I was thinking of storing it as EXIF data or something similar. But most software I've looked at allows me to create my own tags too.

So the questions are: should I store the data in existing EXIF/IPTC categories (like keyword or title); should I use IPTC or EXIF; and is it safe to create my own (safe for portability)? And if creating my own, does it matter if they're associated with the EXIF or IPTC data (or are user-created descriptors off somewhere on their own)?

Answer 1

This sort of data is ITPC data. Exif is data about the image itself, when it was created, modified, what camera, aperture, exposure. Tech specs.

ITPC comes from newspaper wirephoto days. It has keywords, captions, people, copyright, etc.

In theory ITPC can be extended with an xml type set of tag definitions. In practice these are not well supported. Indeed, many photo editing applications strip unknown tags out. You are best to use existing tags.

Even here support is uneven. Use a tool that will write metadata to a sidecar file in addition to incorporating it into the image.

Create a test image with lots of metadata, edit it in your favorite editor and see if the metadata is left intact.

Exiftool is one of the better tools for reading and writing metadata. The interface is arcane, it's not for casual use, but it is fabulous for checking on what other software is doing to your metadata, and can be used to create backups of all metadata.

Answer 2

I have my tags setup using Picasa. I place person, place, comments, GPS and type of wildlife for those types. All the tags are stored in a .picasa.config files in each folder.

When I read the folders for listing the pics on my site, I read them as a file using a Plain text parser. Sometimes scripting / programming language (perl, c#, Java) can also be required.

This discussion can help to move tags to files, using Picasa How can you write/convert Picasa's People tags to the EXIF data?

The good thing is that by separating the metadata from the JPEG, I don't need to update the backup for JPEG when I update the tags. Just backup a single file per folder.

Also different tools can save tags in different ways, so having the tag separated can allow specialized parsing (does involve effort, but atleast its possible)