You can use both, yes. That’s what I do on my own site. CloudFlare is useful, and Photon also optimizes your images, in addition to serving them from a CDN, so using both at the same time will definitely help with your site’s performance.
CloudFlare can do image optimisation via Polish without the overhead on your server, but that would require a Pro plan account. There’s also a tool called Mirage so the images load faster by improving the way browsers load them.
Either way; using CloudFlare will offer you more advantages above this: a CDN, better security, HTTP/2, cache optimisation, etc.
