As it turns out, it's Photoshop.
Yes. The graphics package from Adobe.
Not until today did I really look into it anything, though. I had set out to make myself some animated load progress images for a forthcoming upgrade of my topic navigation system, and figuring it's a blob of JSON being fetched from Del.icio.us (and since it's stylish), I thought I would base it on the JSON logo. My first shot at it ended up like this:
But I didn't realize it was antialiased towards a white background until I was done, and redoing the job from scratch to get it antialiased towards the somewhat darker background I had in mind did not feel like a very amusing prospect at the time. So I recalled the scriptability of Photoshop, and thought I should at least investigate.
Unless I end up fawning over the ExtendScript Toolkit, every time I start poking on it.