Step 1: Login to Google Plus and Go to Google+ settings Option tab at the top right corner.
Step 2: Now you will get the Google Accounts page Opened up. Just Click on Data Liberation Option in left menu side.
Step 3: Click on “Download your Picasa web albums Photos”. Now Google will redirect you in to a Google takeout page. Here you have to again login with your Google Account.
Step4: Now you will get a window with takeout data information. Just click on Choose A service and select Picasa web albums.
Step 5: Click on “Create Archive” button to Download your Google+ Scrapbook Album Photos and Picasa Photo Album.
Once you clicked on the Download button you need to confirm you Google account once again to download your Google+ Album photos. It will download your entire Picasa album along with Google+ Scrapbook Album Photos