Edits made to photos using Picasa's tools are only visible within Picasa. The simplest way to create a copy of an edited image that can be viewed or printed with any program is to use the Save a Copy command.
Open the photo for editing or select its thumbnail in the Picture Library
What happens next depends on the file you selected for copying:
If the file has never been edited in Picasa, no copy is made.
If the file has been edited and is any file type other than a JPEG (.jpg), a copy of the file is saved in the same folder using the same name but with the type and extension .jpg. For example, Birds.tif would result in a Birds.jpg file.
If the file has been edited and is a JPEG (.jpg) file, a copy of the file is saved in the same folder with a sequential number added to the base filename. For example, Birds.jpg would result in a Birds1.jpg file.
Whether the copy will instantly appear in the Picture Library depends on the Folder Manager setting for the destination folder. If the folder is set for Watch for Changes, copies will automatically appear. To make copies appear in a folder set for Scan Once, choose Folder > Refresh Thumbnails or choose this command from the folder's Actions button menu (found in the Picture Library to the right of the folder name).