Picasa is different from other image-editing applications. Edits made in Picasa do not alter the original image file. If you open the file in another program, you'll see the original, unedited picture. Picasa merely tracks edits, enabling you to view and print pictures in it as though the edits had actually changed the file.
When you need to move pictures to another computer or edit them in other programs, Picasa has procedures for saving and exporting your edited images to new files that reflect your edits (see Chapter 9). And when you email pictures directly from Picasa (see Chapter 7), the conversion is automatically performed for you.
One advantage of the way Picasa handles edits is that you can step back through them, removing their effects in reverse order (from most recent to oldest edit) at any time. Open the edited image in Edit View and click the Undo button once for each edit you want to remove. The button's label changes to reflect the specific edit you will Undo.
After you Undo an edit, the Redo button also becomes available. You can click it to reapply the edit you removed.