What are some alternatives?
When comparing Mass Image Compressor and XnConvert, you can also consider the following products
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
FastStone Photo Resizer - Convert and Rename images in batch mode Support JPEG, BMP, GIF, PNG, TIFF and JPEG2000
ImageOptim - Faster web pages and apps.
ImageMagick - ImageMagick is a software suite to create, edit, and compose bitmap images.
Squoosh - Compress and compare images with different codecs, right in your browser
FileOptimizer - FileOptimizer is a lossless file size optimizer supporting AIR, APK, APNG APPX, BMP, CBZ, DOCX...