Hey, my custom image is showing up

[diginc]

By interment, do you mean some sites works and others do not?

I explained how javascript may make custom ad replacement intermittent, in general, here:

Ability to easily ad picture in place of blocked add

Feel free to try customizing the /var/www/html/pihole/ folder index.html and index.js files. Simple ads should get caught by index.html but lots of advanced ad networks serve through javascript (index.js) and you may not have as much success with index.js globally working for all sites. At least that's my assessment with my limited knowledge of front-end web.