A while back I wrote about PNGGauntlet, a windows application that allows reducing image size if they are in PNG format. If you are looking for something that can handle any image format and available through the browser then check out Squoosh.
Squoosh is an image compression web app that allows you to dive into the advanced options provided by various image compressors.
Squoosh offers multiple compression options and defaults to MozJPEG. It also gives some advanced settings that you can use to play around to find one that best suite for your needs. The default compression settings itself provides a huge benefit (69% reduction in size) as in the image above. I use this primarily for the images that I share on this blog.
Squoosh your images!