Windows cjpeg.exe GUI for easy file conversion by drag&drop. Done in AutoIt.
Drop the MozJPEG GUI file in the same location as cjpeg.exe file, launch it, drag&drop your files. Converted files will get barfed out in the same place as originals, with an added prefix. Accepted files are BMP, PNG and JPG.
You can get a Windows binary of cjpeg.exe from https://github.com/mozilla/mozjpeg/releases for instance.
Cuz' sometimes I get tired of keystroking everything in console like some animal.