I have a site that is running on AppFog.com, and they don't have persistent file storage for things like images uploaded through the wordpress media uploader.
The theme I am making for the site includes the Amazon S3 PHP class for some other functionality - and I have that working. What I would now like to do is hook that into the media uploader so that when images are uploaded to my site they also get uploaded to Amazon S3.
So I guess what I want is to know what filters are used when uploading media so that I can hook into them and also upload the images (and the relevant thumbnails) to S3. I tried looking through the source but haven't had any joy so far.
I should point out that I don't really want to use a plugin to do this - but I am happy to learn from a plugin if anyone has any pointers.
Also - since I am using AppFog I don't have access to the server and so can't install anything beyond PHP apps.