sometimes it depends. If you can't download it as anything but a webp. file, copy and paste the image in a word or google document. Then you can right click on the pasted image and it will almost always be saved as a png/jpg image.
Or you copy and paste, right click on it and hit download, or you open it in a new tab and save it. Don't ask me how I know the methods of stealing images from crappy websites.