You told me to try Photon, but I noticed you’re not using it on all your sites. What gives?
When people ask me how to speed up their sites for images, I often recommend Jetpack for the CDN boost. It’s a double edged sword, though. While Photon does two things amazingly well (resize images and put them up on a CDN), it’s hosted on wp.com which means I can’t use it.
What? Why not? No, it’s not that I have something against wordpress.com, it’s that other people do. Like China, Pakistan, and Turkey.
The list is probably longer. But those places, among others, block WordPress.com which means every module of Jetpack that phones home (stats, photon, tiled galleries, LaTeX, related posts, etc) cannot be active on my sites that have a large enough user-base in those places. When I leave those Jetpack features on, the site grinds to a halt for them, which is a terrible experience for my (often non-technical users).
Now that said, I do still use the stats plugins on all my sites with Jetpack. It’s a pretty safe loader to run, and it doesn’t slow the site down terribly (see Issue #566 for the code magic). Photon on the other hand I had to disable entirely because my poor users in China were complaining they could see nothing. I can live with a little delay for loading. I can’t live with an image heavy site not working.
So should you use Photon? Yes! Unless your visitors are blocked by WordPress.com.