See your photo in the comments

I was wondering why every single commenter on my post about Einstein's Power Beyond Imagination quote had a photo"¦except me. It seems a little weird to be the only one with a photo on your own blog. Where do these blog comment photo's come from? To find out, right click on one of the photos and look at the location "“ gravatar. To get your own go to http://en.gravatar.com/emails. You tell them your email address and the picture you want to display.  Then one every blog that uses them, your picture will appear"¦on every blog you have ever used that email on. (this is one reason why most blogs require your email to leave a comment). Pretty neat.