Needing help changing Image Handler for a CDN (Content Delivery Network)

Acknowledged. There are valid reasons why your site can benefit from such an implementation, given your server/traffic dynamics, etc.

But other readers of this discussion need to also note that implementing a CDN for the sake of keeping up with the Jones's so they can use the latest buzz words and sound cool ... is not doing their customers any favors.

And I'll state again that a CDN doesn't guarantee things will be faster. It does decentralize some things, but it increases others. While offloading CPU drain on your primary server is beneficial, it also increases the number of places from which customers must obtain resources, and each of those other places involves increased latency, and on slower connections or slower-powered devices, that can make things worse, not better.

So in short, any technology choice should be made based on the needs of the particular site on the particular day for its particular target audience, and should be regularly reviewed for relevance. This includes both software and hardware (and thus also bandwidth and datacenter connections and geo location, and more), etc.

Remember: while a CDN might help "today", it might be hindering you 2 months from now. Especially if you suddenly attract a lot of visitors from a demographic where their internet connections or mobile devices or PCs are much slower than those of the demographic you attract today.

I do acknowledge that a CDN linked to your own domain (eg: cdn.your_domain.com) carries good weight in terms of trust, and since it is (probably) not the same domain as your store is serving cookies for then there's an immediate speed improvement because of the decreased bandwidth exchanged. Plenty of pros and cons. Part of my overall point is that using a CDN isn't a magic panacea. It's also not an idea to discard either.

Supporting image CDN in Zen Cart can be done, but you'll have a bit of work to do to re-architect things for which Zen Cart by default relies on being able to inspect the images on the filesystem.