replace any incoming image request with my logo:

<IfModule mod_rewrite.c>
  RewriteEngine on
  RewriteCond %{HTTP_REFERER} !^$
  RewriteCond %{HTTP_REFERER} !^https://davidwalsh.name/.*$ [NC]
  RewriteRule .*.(png|gif|jpe?g)$ [F,NC]
</IfModule>