This is a cool project and something I will probably use for some hobby projects.
I would caution against it for anything more than a hobby project as it violates the Cloudflare TOS:
> 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.
For something small, they won't care. If your images make the front page of reddit, you might get shut down.
The main point of this article is to use a Cloudflare cache-everything rule and use that caching to create a free image host. From the article:
> I'd heavily recommend adding a page-rule to set the "cache level" to "everything", and "edge cache TTL" to a higher value like 7 days if your files aren't often changing.
The word on the street is that they will start throttling and contacting you once you hit several hundred TB per month. 
Of course this is still extremely generous and the upgrade plans are usually still several orders of magnitude cheaper than any cloud provider per gb. But don't build a business or hobby project around cf providing unlimited free bandwidth forever.
(basically search HN for cloudflare + non-html)
Should CloudFlare later ban you for the practice, will the random support person you reach unpack the CEO's comments here and ensure nothing changed internally that prevents allowing your continued use and advocate restoring your account for you?
If the perk saves you money, you put that money in savings. Once your budget expands to depend on that perk you are trapped, and when it goes away the pain will be noteworthy.
In words that are more applicable to a business case: You have to have a strategy for when the Too Good To Be True situation ends, because it will, and you have less control over when than you think you do.