Picasa-album-downloader is a project mainly written in Shell, it's free.
Download a private picasa-album with the url you got and without being logged in.
This little script want to help those who get a link to a private picasaalbum and have no account there so that they would have to download every photo manually.
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What you need:
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Usage: ./pad [options] [url]
Simply attach the url you got to the scriptname.