Am I correct, if I presume that Photo stream IS the iCloud storage device for photos?

Photo Stream is a photo sync service between your computers and devices. That's not designed as a storage service, because photos uploaded to Photo Stream are deleted 30 days after adding them to it. If you want to see more limitations, see > http://support.apple.com/kb/HT4858?viewlocale=en_US&locale=en_US

Hi Christina,

To permanently store your photos, you should back them up regularly to your Mac (via iPhoto).

Cheers,

GB