.htaccess

<IfModule mod_setenvif.c>
  # Vary: Accept for all the requests to jpeg and png
  SetEnvIf Request_URI "\.(jpe?g|png)$" REQUEST_image
</IfModule>

<IfModule mod_rewrite.c>
  RewriteEngine On

  # Check if browser supports WebP images
  RewriteCond %{HTTP_ACCEPT} image/webp

  # Check if WebP replacement image exists
  RewriteCond %{DOCUMENT_ROOT}/$1.webp -f

  # Serve WebP image instead
  RewriteRule (.+)\.(jpe?g|png)$ $1.webp [T=image/webp]
</IfModule>

<IfModule mod_headers.c>
  Header append Vary Accept env=REQUEST_image
</IfModule>

<IfModule mod_mime.c>
  AddType image/webp .webp
</IfModule>

towebp.sh

#!/bin/bash

# converting JPEG images
find $1 -type f -and \( -iname "*.jpg" -o -iname "*.jpeg" \) \
-exec bash -c '
webp_path=$(sed 's/\.[^.]*$/.webp/' <<< "$0");
if [ ! -f "$webp_path" ]; then 
  cwebp -q 90 "$0" -o "$webp_path";
fi;' {} \;

# converting PNG images
find $1 -type f -and -iname "*.png" \
-exec bash -c '
webp_path=$(sed 's/\.[^.]*$/.webp/' <<< "$0");
if [ ! -f "$webp_path" ]; then 
  cwebp -lossless "$0" -o "$webp_path";
fi;' {} \;

# USAGE - towebp.sh ~/path/to/your/media/folder

I wrote this to convert entire directories of .jpg and .png files into .webp - making your website fast and beautiful.