Hello John,

> I tried to add new tags to the exif data of my digital images
> using exiv2 with no success.
[...]
> Is there some other way to add tags to an image that
> are not defined in the code already?

You can add unknown tags in existing groups using keys with
hexadecimal tag numbers. Eg "Exif.Image.0x1234"
There is no way to add custom Exif groups (like
"Exif.MyGroup.0x1234"), groups are hardwired to the TIFF structure.
Adding a new TIFF structure element is problematic anyway: other
software wouldn't be able to read it and would corrupt it when writing
other (known) tags.
This limitation does not exist for IPTC and XMP metadata, for these
you can add unknown tags as well as custom groups.

Andreas