What are some alternatives?
When comparing digiKam and XnView MP, you can also consider the following products
ACDSee Photo Studio - ACDSee becomes ACDSee Photo Studio — ACDSee Photo Studio Standard 2018 continues the ACDSee legacy
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Shotwell - Shotwell is an open source photo organizer designed for the GNOME desktop environment.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.
Adobe Photoshop Lightroom CC - Adobe Photoshop Lightroom CC is a commercial photo processor and image organizer.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.