Picasa is a web-based photo storage site so can be accessed from anywhere as long as you can access your PC from wherever you are.

I use it to store all my photos, both those I have taken and those sent to me, and if I want to post them on to someone via email or onto Dogsey, it is easy enough to do.

As I have two external back-up drives, one of which backs up everything automatically at 12 noon each day, the other I manually back up maybe every two or three days, I have never had any problem with Picasa.

Any special photos that I do not want to lose in the unlikely event of my hard drive packing up plus both external hard drives, I save on Dropbox.

I have no idea about iCloud, sorry.

Does Picasa store photo's? -> NO!
Picasa is just a photo editing program that scans and indexes photo and video files that are already in folders on your computer's hard drive disk (i.e. "My Pictures") or your desktop, or anywhere else you place photos and videos. Any photos or videos you see "in" Picasa are the exact same photos and videos that any other program on your computer can see and use.

You control where Picasa looks for photos and videos on your computer by going to the menu Tools > Folder Manager and selecting folders to "scans always." Picasa displays those photos and videos and applies any edits that you make from within Picasa.

Picasa does NOT make its own copies of your photos!

When you install Picasa on your computer, it scans your computer's hard drive to find all applicable photo files. It then displays your photos to you. Picasa does not add, move, copy, delete, archive, back up, upload your photos to the Internet, or do anything else with your photos (other than locating them and remembering where they are) unless you specifically tell it to.

Picaca NEVER moves your stuff around automatically. When you install Picasa, it FINDS your photos. It leaves them right where they were on your computer, and it presents them to you for organization, editing, and sharing. It doesn't "convert" them into anything. They remain in the exact same folders on your disk that they've always been in.

Picasa shows you a "flat" view of the folders (by default) in its folder list. That's just a VIEW of the folders. Nothing on your disk has been changed.
You can view the more normal tree view of the folders by clicking View > Folder List > Tree View. Again, nothing is being moved around when you do this. The photos themselves always remain right where they were on your disk before you ever installed Picasa.

Since Picasa does not physically store your photos, if you delete a photo from a folder while using Picasa, the photo will be deleted from your computer.

Picasa is always working directly with the photos on your disk. Once the photo has been deleted from your computer, Picasa will no longer be able to show you the picture.

If you delete a photo from a folder using Picasa, it's exactly like deleting the photo from the folder using Windows Explorer.

Sometimes, people make a really bad assumption that Picasa has somehow created its own new copies of all the photos. So they delete everything they see in Picasa. What they're doing at that point is really deleting the real, original photos from their real folders on their disk. That's a HUGE mistake. Try a photo recovery program to get your photos back - some programs are listed here (the link will take you further down this page. Please come back up and continue reading where you left off).

As Picasa is a part of Google it is web-based, so as long as you are able to get into your PC account via another computer, you will be able to find them

best free storage for safely storing digital photos? Not linked to your own computer but somewhere you can safely download all your photographs and access from any computer.

Thanks Pat, and sorry if I mis-understood you. I have less than one thousand photos on Picasa 3 and they are all copied onto both my external hard drives. I do not use Picasa Web Albums as they would, from what I understand, have to be on a specific Google account. As I have a number of different Google accounts [I keep separate accounts for separate things], I do not want to tie my photos up with any particular one.

For me, as a basic user of photographs and storage of same, Picasa 3 does what I need. For someone who takes and needs to keep thousands of photographs - a professional photographer or web designer, obviously they would need far more than I do.

I apologise for confusing Picasa 3 and Picasa Web Albums.