Digikam
Useful settings
Collections -> Ignored Directories -> #recycle (for synology)
Metatdata -> Behaviour -> Use Lazy Synchornization: makes you confirm the changes before writing them below. Useful when working on lots of pictures (eg face recognition)
Metatdata -> Behaviour -> Face tags + geolocation information on
Metadata -> Sidecars -> write and read on.
Miscellaneous -> Behaviour -> Scan for new items at startup, fast scan, detect faces in newly added images. Fast scan will not detect items changed in external programs.
Miscellaneous -> Behaviour -> Initially select the first item in the album
On the bottom right, to the left of the zoom level, there is a little triangle with a status bar when digikam is operating. Press the triangle to see what it is doing.
Faces
In the preview you can select show face tags on and off in the top left of the preview picture
To remove a face, right click on a picture, remove tag and then select the person to remove
You can make a face a thumbnail by rightclicking on a face in the People tab
You can see all the faces of a person in the people tab. You can see the whole picture in the Tags tab under People
To no longer scan for a person, you can right click the person in the People view, click Unmark tag as face, continue, but BE CAREFUL do NOT remove the tag corresponding to this face tag from the images! (so answer NO) You will then be able to find the tag still in the Tags list, but no longer in the people view.
To reset thet training data (If you have edited a faces collection and removed people that don't belong), Tools -> Maintenance -> (Albums) -> face Engine management -> rebuild all training data
Maintenance
Tools -> Maintenance -> Perform Database Cleaning
This should be done periodically to ensure everything is up to date and compresses the database. Digikam will stop responding during this cleaning as it doesn't want any conflicting inputs. This can take a long time!