Apps to Built-in Image viewer

GPicView is a streamlined and exceptionally fast image viewer designed for the X Window System, particularly popular within lightweight desktop environments like LXDE. It prioritizes speed and simplicity over a complex feature set, making it an ideal choice for quickly browsing and displaying image files.

Nomacs is a fast and lightweight free, open-source image viewer offering a wide array of features for diverse image formats, including RAW and PSD. It provides essential editing tools, batch processing capabilities, and extensibility via plugins, making it more than just a simple viewer.

F-Spot is a discontiued, but capable photo management application specifically designed for the GNOME desktop environment. It offers a range of features for organizing, editing, and sharing personal photo collections, supporting various image formats.

Darktable is a powerful, open-source and free photography workflow application and raw developer, offering professional-grade tools for managing and editing digital negatives. It's a non-destructive editor designed by photographers for photographers.