JPEGOptim is a free open source Linux and Windows program that optimizes the compression of JPG images. It was developed by Timo Kokkonen and first released in 1996. The program has several options, most of which require a basic understanding of image formats and compression, but the default options will almost always yield better results than a typical graphic program. The program can be run to optimize the Huffman tables (and retain the original quality), or re-encode the image at a higher compression level, and lose quality.
To use the program with its default settings, simply drag and drop a JPEG image onto the jpegoptim.exe file.
I found this program in the late-2010s while looking for a JPEG equivalent of PNGOut. I use it for all the images I upload to my web sites and for large graphic projects I've done in order to save space.
Although the developer is still adding to the program, he doesn't maintain builds, even for simpler platforms like Windows, so you have to compile the program from source to get the latest version, although SourceForge still has older binaries available.
- sourceforge.net/projects/jpegoptim - Source Forge with older binaries.