WebP is an image file format developed by Google. Since there are not many programs that support WebP, you might sometimes want to convert a WebP file to other common formats like PNG.
Converting WebP to other image file formats is easy using the WebP library provided by Google. Note that using the WebP library package from the Ubuntu repositories did not work for me. Only a few popular formats are supported, including PNG and BMP. Most notably, the JPG format is not currently supported.
To convert a WebP file:
$ sudo apt install webp
Alternatively, you can also download the libwebp archive file that matches your system from here. Unzip the archive file.
$ dwebp foo.webp -o foo.png
Tried with: LibWebP 0.3.0-3 and Ubuntu 14.04