Hi @qwik3r!
This is Joseph from Imagify, and I’ll gladly assist you here!
The rewrite rules are there to allow for display of WebP images for users of browsers that support them, and to provide fallback to JPG or PNG images for those that don’t.
So what this means is that if you are using a CDN, the rewrite rules will not work to allow for WebP image display on your site, as images must be on your server for the rewrite rules on your server to work for them. This is not the case when you are using a CDN.
So if you use the “Use rewrite rules” option and a CDN, the result will be that images will still display in their JPG or PNG format, but they will not be swapped out for WebP images for users of browsers that them.
If using a CDN, your only option would be to switch to the “Use <picture> tags” setting in Imagify settings (and remember to include the CDN URL in the input field).
Also of note is that if you are a WP Rocket user, there is also a setting that allows for WebP display with CDNs.
Hope this explains this issue for you, but please let me know if you have any further questions. We are always glad to assist!
Best regards,
Joseph