I may be wrong, but I think there is a big difference between photon and at least the free version of cloudflare. Photon claims to request a resized version of your image (to suit the space it will be displayed in) while cloudflare simply caches the file as is, and returns it. This may be significantly larger than is needed for the display device, taking longer to download, and occupying more of the available cache space on the device (and thus flushing more data from the cache). If the viewer is using a high spec PC on a fast fibre internet connection, then the difference won't matter, but for a handheld mobile device it may matter much more. As well as taking much longer to download the first time, it would consume much more of the device's limited space for caching internet files, and itself be cleared from cache on the next similar page view.