TL/DR: We are going to install the official executable for dwebp, if you do not want to waste your time just https://ezgif.com/webp-to-png.

Webp is a very small image format provide both lossy and lossless, where you may happen to get it when you drag an image to download.

https://developers.google.com/speed/webp/

Official Website

Mac

If you are a mac user, you can also try using my Drag and Drop dwebp script:

https://gist.github.com/jimmyctk/c246cb9d64e2058b07a75ef1434d2475

Simply execute it, and it will ask you to drag and drop the files you want to convert, and Press enter, volia!

Pre-requisite

If you are running on Mac, you got 3 ways to install dwebp:

1. Install via homebrew

brew install webp

2. Install via MacPorts

sudo port selfupdate
sudo port install webp

3. The hard way (which I wont go through)
https://developers.google.com/speed/webp/download

Windows

I have also another bat file to Drag and Drop:
https://gist.github.com/jimmyctk/18dcb0c49cadbbd9c41663bedab13b07

dwebp.bat "C:\path-to\dweb.exe" "C:\path-to\file.webp"

Pre-requisite

1. Download the executable
2. Decompress the file and put the folder somewhere nice
3. Press “Win+R” and type SystemPropertiesAdvanced, Enter
4. Open the option Edit the system environment variables
5. Click Environment variables... button
6. There you see two boxes, in System Variables box find path variable
7. Click Edit
8. a window pops up, click New
9. Type the Directory path of your .exe or batch file ( Directory means exclude the file name from path)
10. Click Ok on all open windows and restart the command prompt