Get uploads from live domain if they do not exist locally — Must be added to wp-content/uploads/.htaccess
RewriteEngine On
RewriteBase /wp-content/uploads/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{HTTP_HOST} ^localsite\.test$
RewriteRule ^(.+)$ http://livesite.com/wp-content/uploads/$1 [L,R=301,NE]