DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
ACDSee - ACDSee is an image viewer that uses very little system resources, and it has a small, sleek size that won't take up much space on your system.
Darktable - darktable is an open source photography workflow application and raw developer.
Photoscape - high quality photo editing software, that enables you to fix and enhance photos.
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
Polarr - MacOS, Windows, iOS, Android and online photo editing tools & free photo editors.