Use Google Maps in Picasa to place your photos on the map. To geotag a photo, follow these steps:
- Select the photos you'd like to geotag.
- Click the Places button in the lower right corner of Picasa.
- Navigate to or search for your location.
- Click the green marker button to add a new place for selected photos. Move the green marker to the spot where you took the photos.
- Click the OK button to finalize the geotag.
You can also drag-and-drop photos directly onto the map.
Picasa will write the longitude and latitude to the photo's EXIF metadata. You can view this data (GPS Latitude and Longitude) by right-clicking (Windows) Control-clicking (Mac) a geotagged image in Picasa and selecting Properties. Geotagged photos are marked with a 
icon when viewed in Picasa.