Hmm...not sure I approve of the term "lurking about", but anyway...
1. Yes, anyone can look at and/or print a copy of any image in the Gallery. If that's a problem for any member then don't post your stuff in the Gallery.
2. The links under
Share This Photo are to submit a link to the photo to various online communities. This is the description of Digg that appears on their About Us page:
Digg is a user driven social content website. Ok, so what the heck does that mean? Well, everything on Digg is submitted by our community (that would be you). After you submit content, other people read your submission and Digg what they like best. If your story rocks and receives enough Diggs, it is promoted to the front page for the millions of visitors to see.
3. Sending an image as an e-card sends an email containing a link to the image you choose, along with a customisable message. As bedlam123 says, give it a try - you won't break anything.