I'm brand spanking new to ZP. One feature I would really like in a photo gallery is to be able to store an image description in the image file itself, so that the description goes with the file on a download. From my searching, it appears that ZP can read metadata from photos. And I think there is a plugin(s) that can be used to edit metadata. But is there any way to write image descriptions to the image files, preferably in bulk?

I've never used ZP to write meta data to files. I've always used Irfanview https://www.irfanview.com/ which has a plugin to read exif and IPTC tags ( METADATA plugin) as well as to write IPTC tags and it does have a bulk mode. There are probably other tools that can do this also. ZP can then read these tags using the HTML_META_TAGS plugin.

Note: I'm still on version 1.5.7 but the current version should have the same capabilities ( I should really try and update some day. )

Zenphoto does not write meta data to image files and it is not planned, the full/original images uploaede are generally never changed by Zenphoto (except cleaned filenames possible if that is enabled). Images should have metadata already embedded.

Of the two supported image libraries GD and Imagick only Imagick theoretically could do that at all. Also, the xmp-metadata plugin supports exporting xmp metadata to a sidecar file.

@markrh:

Note: I'm still on version 1.5.7 but the current version should have the same capabilities ( I should really try and update some day. )

You really should! 1.5.7 is already over five years old and possibly you have even some unfixed (minor) security issues! And we are heading to version 1.7 already! The longer you wait the more work you will have . And at some time your host will force you to do if older PHP versions are disabled. 1.7 will take some time still but for sure will be the last version to officially support PHP 7.