Picasa has "Sync to Web" functionality, which allows you to automatically sync photos to Picasa on your Mac computer. If you publish a photo album in Picasa Web Albums, then you don't need to re-upload a photo manually. You can use 'Sync to Web' functionality to change a caption, crop a photo, add a name tag or add a location. to automatically sync photos to Picasa Web Albums, download and install "Picasa for Mac" application on your Mac. Open it and select an album or a folder of photos. Toggle on "Sync to Web" button located at the top right of the page and sign into your Google account. Now, configure your sync settings i.e. size of the photos, whether they should have watermark or not, they should be private or public. Once you have done this, you can automatically sync photos to Picasa on Mac.