Prevent Images on Cloud Storage from Rendering Outside of our Website

We are trying to prevent images from rendering anywhere but from within our website.
We want to prohibit rendering with Direct URL pasted in a browser and Hot-linked on other websites.

We use Cloudflare DNS and have our images in Cloud Storage set-up as a sub-domain with a separate IP address from our main website.

I am trying to use Cloudflare Rules to lock down the images from rendering outside our site, but having some trouble getting it to work. Here is the CF Rule I am trying pasted below:

Any help or guidance will be appreciated.