The other option is just make the changes and Picasa will automatically save the original in a new sub-folder to the one in which you are working. It will retain the new edited one in the main folder and will allow you to revert by removing all the editing you might have done. Only when you press Save Changes at the top of the Picasa album will it keep the current editing. Even then you can go into Explorer, delete the edited version and copy back the original from the sub-folder.
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Do you know that we're all in line for succession to the throne? Really?
Well, if forty-eight million, two hundred thousand, seven hundred and one people died I'd be Queen.