Hi

I have done something close to what you require, but you will need to be confident enough with accessing a database using phpmyadmin and getting your hands dirty a bit! My problem was to transfer captions, titles and geotagging information from Piwigo into the EXIF/IPTC information for photos. (The context of my work was copying info originally entered on Flickr, but that is not really relevant). I found it was too complex to deal with normal tags, primarily since there can be a variable number of them for each photo.

As background, it is important to understand, as I see it anyway, that if you use Piwigo to enter captions and tags etc, then this information is stored in the Piwigo database and NOT in the photo file itself (unless it was there before the photo was uploaded). If you want to move information entered via Piwigo into the jpg files, then my procedure is based on this (it may not be the best method but it worked for me): (1) use phpmyadmin to extract the appropriate fields from the Piwigo database for the relevant photos and export this information to your computer in a suitable format, 1 row per photo - csv for MSExcel is fine (2) open the csv file, check it looks ok, edit if necessary, and add a header row which gives the correct EXIF names to each field (3) use the batch downloader plugin to download the relevant jpg files from Piwigo, to ensure consistency of filenames (4) merge the fields from the csv file into the jpg files using exiftool from the command line.

This worked for me, and many files can be done in one go. Of course, only do this if you feel reasonably confident, and try it on a test database first and not your live one!

Martin