One can created a test custom scanner in "Plex Media Server/Scanners/Photos/Custom Really Awesome Photos Scanner.py" and the picture library creation popup allow to select it so we can have a custom scanner for photos... The scanner cannot populate much metadata, just the year/date/title, but could create different folder categories for the pictures shall the need arise.
The agent would be the one populating the metadata info from the EXIF/XMP metadata and more especially the summary and title fields. The presence of filters in the Plez web ui for Photos library seem to indicate some undocumented level of support for metadata. What oculd be done with a scanner is populating the title with the exif data, but that doesn't seem that useful and would require a python library that accept being loaded by the scanner....
Photo scanner source:
Dev center down but link up https://web.archive.org/web/20140107030832/https://dev.plexapp.com/ (Thanks madman) but little on scanners but since i wrote my own i could possibly do it
os.path.getmtime would give last modification time
I don't mind doing a scanner, but all i can give you so far is a way to output logs in a custom log inside Logs folder. This could give a head start to somebody...
Photos are scanned by the standard Scanner (look here: https://github.com/plexinc-plugins/Scanners.bundle/blob/master/Contents/Resources/Photos/Plex%20Photo%20Scanner.py ) and additional metadata is extracted by the media server during analysis. There is not a separate agent like there is for other types of media.
The Plex agent seems to extract the EXIF metadatas, but it doesn't extract the XMP or the RDF...
No agent possible so the margin for manoeuvre is reduced