CORS stands for Cross-Origin Resource Sharing.
In order to share your images across domains you'll need to set CORS headers.
This is a security feature of browsers. Setting the header appropriately will allow for untrusted clients to display your images. If you don't the browser will issue a warning (often via the address bar) or fail to load the image completely. Is this correct for CORS?
Here are some tips on how to enable CORS headers for various servers: https://enable-cors.org/
Here's more in-depth information about how CORS works: https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS