I would like to save the photos on iCloud
iCloud is very different from MobileMe. It does not store photos permanently. It will allow you to stream your photos to your devices, but it does not replace your iDisk.
What the Photo Stream will do: If you take a photo on a device it will upload it to the stream and buffer it for a month in iCloud, so that you can import it from iCloud to your other devices. After a month it will vanish from iCloud. To use the basic Photo Stream you need Mac with OS X Lion v10.7.5 or later and iPhoto 9.2.2 or Aperture 3.2.3 or later, see: iCloud: Photo Stream FAQ
Shared Photo Streams, available with MacOS X 10.82 and later, will allow you to create separate Photo Streams without a time limit, but also only a limited amount of photos. For Shared Photo Streams you need: Mac with OS X Mountain Lion v10.8.2 or later and iPhoto 9.4 or Aperture 3.4 or later
iCloud: Using and troubleshooting Shared Photo Streams
-- Léonie