Google's image organisation and editing program Picasa makes it easy for Intel-based Mac users to manipulate photos and share them with friends via e-mail, social networking sites and even printed books. Functionality to import photos from Apple's iPhoto application is a simple one-step process, but moving photos from Picasa to iPhoto is slightly more involved. Due to the way Picasa handles edits, photos are best duplicated by being exported to a folder before being imported into iPhoto.
Open Picasa by double-clicking its icon in the Applications folder or clicking its Dock icon.
Select the photo or photos you would like to share with iPhoto.
Select "Export Picture to Folder..." from the File menu, and choose an export location by clicking the "Browse" button.
Click "Export" to save the photo or photos to the desired folder.
Drag that folder from the Finder onto the iPhoto icon on your Dock. iPhoto will automatically open, and the folder will be imported as an "Event."