Picasa Web Albums allows you to share photos, videos and albums with others. It has "Album Visibility" which allows you to control who can see your albums. There are 3 options i.e. "Public", "Limited, anyone with the link" and "Only you". You can unshare photo album by changing the album visibility.
To change a photo album visibility, go to your Picasa Web Albums account and click "My Photos" tab. Browse the photo album which you want to unshare. Select "Actions" tab and then select "Album properties". Select your visibility option in "Visibility" and then click "Save changes" button.
If you have shared a URL with someone, then you need to rename the album ot add the "Login required" option.
Quick Tip to ensure your Photos never go missing
Photos are precious memories and all of us never want to ever lose them to hard disk crashes or missing drives. PicBackMan is the easiest and simplest way to keep your photos safely backed up in one or more online accounts. Simply download PicBackMan (it's free!), register your account, connect to your online store and tell PicBackMan where your photos are - PicBackMan does the rest, automatically. It bulk uploads all photos and keeps looking for new ones and uploads those too. You don't have to ever touch it.