How to block all external elements loading using .htaccess?

Hello,

i want to block loading of all elements loaded from external sites. For example embeding images that are hosted on different domains.

My failed attempt is:

# Disable external content
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http(s)?://(subdomain.)?mydomain.com [NC]
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?mydomain.com [NC]
RewriteRule \.(jpg|jpeg|png|gif|bmp|webp)$ - [F]

Code (markup):

In last line i have mentioned some extensions though i would prefer blocking everything, except for example filename externalcaptcha.js and otherexternal.file

Thank You