FastStone Photo Resizer Alternatives for Mac OS X

PhotoBulk is a powerful yet simple bulk image editor for macOS. It allows users to perform multiple editing operations on hundreds or thousands of images simultaneously, including watermarking, optimization, resizing, and renaming, all through an intuitive drag-and-drop interface.

ImageMagick is a powerful, free, and open-source software suite designed for comprehensive manipulation of both raster and vector images. It offers a vast array of tools for displaying, converting, editing, and processing image files, accessible primarily through a compelling command-line interface.

XnConvert is a robust and free cross-platform batch image processing tool designed to handle multiple image manipulation tasks at once. It supports over 500 file formats and allows users to combine more than 80 distinct actions, making it an indispensable asset for photographers, graphic designers, and anyone requiring efficient bulk image editing.

GraphicsMagick is a powerful and efficient open-source software suite for image processing. Designed for command-line use and integration into scripts and applications, it provides a comprehensive set of tools for manipulating, converting, and performing various operations on image files in numerous formats.