I would like to expand the list of editable IPTC-Fields when you edit images (admin-edit.php).
Now:
[code]$image->setTitle(process_language_string_save("$i-title", 2));

$image->setDesc(process_language_string_save("$i-desc", 0));
$image->setLocation(process_language_string_save("$i-location", 3));
$image->setCity(process_language_string_save("$i-city", 3));
$image->setState(process_language_string_save("$i-state", 3));
$image->setCountry(process_language_string_save("$i-country", 3));
$image->setCredit(process_language_string_save("$i-credit", 1));
$image->setCopyright(process_language_string_save("$i-copyright", 1));[/code]

How to add editable fields like:
Artist, Image Caption, Image Credit, Byline, Byline Title, Copyright Notice

The fields I like to add to be editable are shown in the Metadata field.

How to make this feature a Plugin without hacking the ZP-Core code?

Thanks for your advice.

Meta data fields are not editiable as they are metadata fields stored in the full images. Zenphoto cannot write changes to the images itself anyway.

It is however possible to add custom fields via a filter. Actually splitting the existing custom field. Another way would be to use the plugin_storage table to create real extra fields.
Please see the plugin tutorial about filters.

Really, your best bet is to edit those fields in the image itself before uploading it. There are several tools that might be used for that. For instance the Adobe Bridge software.

Editing them in the image makes the edit "permanant" in that it stays with the image even if you loose your database. Also it is permanant in that it will not get overridden if you do a refresh metadata.

While it would be possible to edit the fields, I think it ill advised for the above reasons.