I'm afraid you are in for a nasty surprise: CloudFlare specifically forbids using it mostly as an image/video CDN unless you are on the Enterprise tier (clause 2.8 in the Terms).
I found it out the hard way a couple of years ago when I was helping with maintenance of a pretty large image hosting website (we got to 1-2Pb/mo range). CF may not pay attention to you while you are small, but when they do, it's going to cost you.
"2.8 Limitation on Non-HTML Caching
The Service is offered primarily as a platform to cache and serve web pages and websites. Unless explicitly included as a part of a Paid Service purchased by you, you agree to use the Service solely for the purpose of serving web pages as viewed through a web browser or other application and the Hypertext Markup Language (HTML) protocol or other equivalent technology. Use of the Service for the storage or caching of video (unless purchased separately as a Paid Service) or a disproportionate percentage of pictures, audio files, or other non-HTML content, is prohibited."
They are willing to serve as your CDN if you don't make them front too much image or audio traffic and you don't make them front any video. Their free tier is for non-media-focused sites only.
I wonder if that's just for specifically image hosting websites like your case. Parent comment and my previous experiences seem to imply that embedded media is okay.
Even then, just a few terabytes of traffic will make Cloudfront reach the thousands.
