PhotoQt
PhotoQt is a free and open source multiplatform, fast and simple, yet powerful and highly configurable image viewer
Nomacs
Nomacs – free and open source multiple platforms fast image viewer with additional editing functionality
Fotoxx
Fotoxx is a free open source Linux program for image editing and collection management
Phototonic
Phototonic – free and open source software for viewing and organizing images with simple editing functions for Linux
XnView MP
XnView MP – free and cross-platform, versatile and powerful software for viewing, organizing, and editing photos
RPhoto
RPhoto is a lightweight free and open source software for easy photo handling on Linux and Windows
qView
qView – free and open source cross-platform full-featured minimalistic image viewer
Gwenview
Gwenview – free and open source software for viewing images with simple editing features
Eye of GNOME
Eye of GNOME – free and open source Gnome image viewer for Linux
digiKam
digiKam – free and open source program for viewing, organizing, and editing photos