google apt source for debian

On an APT-based system (Debian, Ubuntu, etc.), you must download the key and then use apt to install it and refresh your package indexes.
For more information on Google's package signing key, see the Signing Key page.

Run these commands as root:

wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | apt-key add -
apt-get update  

Recent versions of apt-get will automatically attempt to verify packages on download. If an appropriate key is not found or if the package is corrupted, you will get a message like the following:

WARNING: The following packages cannot be authenticated!
packagename  

Add the following rule to e.g. /etc/apt/sources.list, or if your distro has the /etc/apt/sources.list.d/ directory, add it to a file called google.list in that directory:

# Google software repository
deb http://dl.google.com/linux/deb/ stable non-free  

then use apt as usual, e.g.

sudo apt-get update
sudo apt-get install picasa