Caesium is an image compression software that helps you store, send and share digital pictures, supporting JPG, PNG, WebP and TIFF formats. You can quickly reduce the file size (and resolution, if you want) by preserving the overall quality of the image.
I might add a link to the README for older versions. You can download it from here or here.
Anyway, I strongly advise against using the 1.7.0 as it is no longer maintained. If you need to convert from/to formats, you can use the 2.3.0-beta you can find here.
Readme.md:
Where can I download v1.x for my old PC?
NB. I think it might be possible to run v2.x on Win7, despite Qt6 incompbatibility, thanks to these compatibility hacks