YOGA Image Optimizer is a graphical tool to convert and optimize images (reducing file size). It supports several formats as input and can generate optimized JPEG, PNG and WebP (both lossy and lossless).
You will be able to save about 30 % of space on JPEGs and 20 % on PNGs. Optimizing a WebP image will save you only few percents... but converting a JPEG to a lossy WebP can reduce image size to a half and converting a PNG to a lossy WebP can save you 35 % on average.
YOGA Image Optimizer is available on Linux and Windows.
Instructions for Linux: https://github.com/flozz/yoga-image-optimizer#install
Windows Installer: https://github.com/flozz/yoga-image-optimizer/releases
If you need a command-line interface, please note that YOGA Image Optimizer is based on YOGA, a Python library and a CLI tool that, of course, can optimize images, but also 3D models.
Official Web site: https://yoga.flozz.org/