According to my inbox, you're absolutely right, though this is a form of spam that I hadn't seen until your question came in. Hmmm... :-)

As you can see in the screenshot below, spammers continue to exploit social networks to worm past those pesky spam filters that prevent their victims, uh, potential customers from seeing their messages:

The dilemma is that you probably don't want to report this as spam in Gmail (where I received the message) or another service because then legitimate photo album sharing invitations from your friends and family will be blocked too. Not good. On the other hand, if this becomes a real problem and you start seeing lots of this sort of spam then you will need to take some steps because it's easy for spammers to create dozens, hundreds, or thousands of groups, fake email addresses, photo albums, whatever, so that they can keep wiggling through overly focused spam filters.

I am hoping that Google will step up to the plate quickly with this problem and figure out an account verification solution that will make this sort of sneaky abuse of their service much more difficult.

With some irony, we're at a point now where instead of us gaining anonymity with the Web, we're probably going to see more identity verification, where they'll physically mail a postcard with a verification code to confirm your mailing address, where email addresses will have to be tested, and perhaps even something like a national identity card will come into play somehow too.

I wish you luck with these Picasa spam messages, but I'm afraid I don't know the best way of preventing more of them in the future. Perhaps a reader can offer some sage advice?