Saving Edits: Saving photos
Picasa is designed to keep your original photos safe when you save your photo edits. This is done by creating a new JPEG file that's a copy of the original with your edits applied. The original photo is never altered, but depending on how you save the file, its location on your hard drive may change. Here's a brief overview of the different save options in Picasa, based on how they affect the location of your original photos.
Move your original photo
When you use the Save to Disk and the File > Save options, Picasa creates a copy of your photo with all edits applied and moves the original to a subfolder called '.picasaoriginals'. This subfolder is hidden on your computer and isn't visible in Picasa. This automatic backup lets you undo or revert your saves.
Save to Disk
File > Save
Keep your original photo in its current location
Unlike Save to Disk and the File > Save function, the following options don't move your original photos. These options create and save a new copy of your photo with all edits applied, leaving your original photo unmoved. The new copy with edits applied is saved to a different location depending on the option you choose.
Export
File > Save a Copy
File > Save As