How to Open PNG Images in Picasa
- Open Picasa.
- Click the Tools menu in Picasa and select Options.
- Click the File Types tab at the top of the Options window.
- Enable PNG image support by clicking the PNG check box and clicking “OK.”
- Click the Tools menu and select Configure Photo Viewer.
- Click the PNG check box in the Photo Viewer Configuration window to open all PNGs in the Picasa Photo Viewer by default, if desired, and click “OK.”
Adapted from a post on eHow.com