Picassaweb is a way of sharing photos, and you can "publish" a Picassaweb album to your own blog or website with the simple linking tools provided. A second tool in the Picassaweb bag of tricks is the ability to upload to an album via email. You simply address the email to a secret (???) email address with the name of the album as the subject. It doesn't have to come from your own email address. It can come from anywhere and anybody as long as they know your secret address at Picassaweb.
So the problem is that these two Picassaweb tools, while incredibly powerful and easy on their own can create an dangerous security problem for the Picassaweb account holder if he isn't very careful.
PicassaWeb (Google) has implemented no security whatsoever, so it is possible for anyone that knows the "secret" address to upload photos which could then go onto the website automatically... without even any notification! Goodness knows what might appear on the person's website if an unfriendly person discovered the address.
Scary but true.