Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
GIMP - GIMP is a multiplatform photo manipulation tool.
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.
Ralpha Image Resizer - High-speed image batch conversion tool