Image Roll is a simple and fast GTK image viewer with basic image manipulation tools.
Ristretto
The Ristretto Image Viewer is an application that can be used to view, and scroll through images.
RNote
A simple drawing application to create handwritten notes.
nomacs
nomacs is a free, open source image viewer, which supports multiple platforms. You can use it for viewing all common image formats including RAW and psd images.
imeditor
Simple & versatile image editor.
Dupeguru
dupeGuru is a cross-platform (Linux, OS X, Windows) GUI tool to find duplicate files in a system.
Coreimage
An image viewer for C Suite.
Detwinner
Detwinner is the simplest and the fastest tool for removing duplicate files from your Linux PC.
Curtail
Curtail (previously ImCompressor) is an useful image compressor, supporting PNG and JPEG file types.
Identity
Compare images and videos