Thanks. Yep that's correct, I'm an independent developer.

All the effects are created live in the app itself, there's no server-side image processing done. It's true that the app simply uploads images straight to Facebook without touching my server (unlike Twitter, which is required due to the way their API works) - and thankfully it doesn't have to, or I doubt it would cope with the load. Facebook must have loads of servers purely for processing image uploads. My back end is simply Apache+PHP.

I hope to blog more about my experiences in the future too. Thanks for the feedback.