digiKam

digiKam manages photo collections that stay as ordinary files in ordinary folders. It indexes those folders into a database — SQLite for a single machine, MySQL or MariaDB when the catalogue is shared — and layers albums, hierarchical tags, ratings, colour and pick labels, captions and saved searches on top. Metadata is read from and written back to EXIF, IPTC and XMP, so the information travels with the file.

Beyond cataloguing there is face detection and recognition for grouping people, a map view driven by GPS coordinates with the option to write coordinates onto images from a GPX track, and searches for duplicate or similar pictures. An image editor handles curves, levels, white balance, noise reduction, lens correction and perspective, with raw decoding done by libraw. The batch queue manager applies the same chain of operations, renaming rules or format conversions across many files at once.

digiKam comes out of the KDE community and carries a wide feature surface, so the first run takes some setting up.