Allow users to "upgrade" Large images to Original sizes
Since you added the new Original size dropdown, I'd love to update the Picasa versions to use the full-sized images.
Please add a way to reupload the higher resolution photos. (Or downgrade them, if the user wants to save on quota.)
It appears to be possible using this API endpoint: https://developers.google.com/picasa-web/docs/2.0/developers_guide_protocol#UpdatePhotoOnly
It looks like you're using PHP and unfortunately the PHP docs for the Picasa client library don't have some way to do this. But I assume that doing the bit of code that uses PUT instead of POST should not be too difficult.
Similar to “Allow Restart” idea. Involves allowing upgrade of image size later.
Simon Law commented
Yes, this is a valuable feature for people who have tried out the service, liked it, and have paid for extra Google Storage.