Mapping IPTC to ALT Text

Thanks for your question, and thanks as well for taking the time to find and study the earlier topic you referenced above. The IPTC extensions are outlined in this earlier topic, too:

Syntax for XMP fields?

You can adapt the rule described in the topic you found as follows:

1. Go to the Settings/Media Library Assistant IPTC/EXIF tab.
2. If you want to apply the rule to new items as they are uploaded, check the “Enable IPTC/EXIF Mapping when adding new media” and “Enable IPTC/EXIF Mapping when updating media metadata” boxes.
3. Locate the “ALT Text” rule entry in the table and click the “Edit” rollover action.
4. In the “IPTC Value” dropdown control leave the default, “- None (select a value) -” value in place.
5. In the “EXIF/Template Value” text box, enter template:([+xmp:Iptc4xmpCore.AltTextAccessibility+]) .
6. In the “Priority” dropdown, select “EXIF”.
7. In the “Existing Text” dropdown, select “Replace” to replace existing term assignments or “Keep” to retain any existing values.
8. In the “Status” text box, select “Active”.
9. Scroll down to the bottom of the screen and click “Update”.

Note the changes in steps 4-6, which show how to access the extension fields in a mapping rule.

I am marking this topic resolved, but please update it if you have any problems or further questions regarding the above suggestions. Thanks for your interest in the plugin.