ImageMagick is great for converting images and stuff… so you don’t have to go to an image conversion site and do the upload/download dance.
$ sudo apt install imagemagick
$ convert image.webp image.png
$ convert image.png -resize 50% shrunk-image.png
$ convert image.png -resize 200 image-200px.png
This is all for ImageMagick v6. Apparently ImageMagick v7 is out but Ubuntu is still distributing ImageMagick version 6 so that’ll do for now.
In v7 apparently the command switched from convert to magick. Now you know!