What are some alternatives?
When comparing Caesium Image Compressor and FastStone Photo Resizer, you can also consider the following products
ImageOptim - Faster web pages and apps.
XnConvert - XnConvert is an easy image converter for graphic files, photos and images available on Windows...
pngquant - command-line utility and library for lossy compression of PNG images
Phatch - Phatch = Photo & Batch!
ImageMagick - ImageMagick is a software suite to create, edit, and compose bitmap images.
Image Resizer for Windows - Lets you resize images by right-clicking.