Maybe it’s not THAT obvious, but it’s fairly simple as you’ll see.
You’re not going to use a Webflow image element, but a custom code component.
Your custom code component MUST be placed inside of a Collection list OR inside of a CMS Template Page.
Inside of your collection, you’ll add a URL field if you want to use the complete URL (ie: http://www.mysupercustomCDN/images/image.jpg) or, if most of the URL is predictable (doesn’t change), a text field. In the URL field you’ll put the complete address for the image (http://www.mysupercustomCDN/images/image.jpg), and on the text field, if you chose it, you’ll only put the name of the file (image.jpg).
http://vincent.polenordstudio.fr/snap/3i27w.jpg
Let’s consider you’re using the text field and add only the name of the image to the CMS items.
Drag a custom code component inside of the Collection List or Template Page.
Add an HTML code for an image
http://vincent.polenordstudio.fr/snap/bom6h.jpg
Select the part of the code that will change (the file name) and click on +Add field, then select your CMS field
http://vincent.polenordstudio.fr/snap/mzq62.jpg
Now you have a dynamic URL that will display your CDN image referenced in the CMS collection
http://vincent.polenordstudio.fr/snap/0mszq.jpg
You want to easily style this in Webflow? Add a class in the code.
http://vincent.polenordstudio.fr/snap/utayg.jpg
Now drag any image in the Designer and add the class to it
http://vincent.polenordstudio.fr/snap/zmzjw.jpg
Style it as desired and delete it. Your CDN image will be styled the same way.