The same can be said by any forum post you've ever made! Big brother internet spiders are watching you......
Its not very often you can say 'Big brother internet spiders' in one sentance often.
You'll have to have words next to the image ie. forum name, email address, forum text or just the image name to make a random and often small image to be recognisable in real life.
You can take avatar pics from anywhere and they don't have to be of yourself. Take heart that your bottom pic could of been anybodies.
But there are two blokes in your avatar Jags. One is kneels before you with two hands cleary visible. Who's is the third hand that is creeping up the bottom of your leg there?
Google and most of the other search engines will crawl and digest every written word posted on the Internet and images get associated with with alt text and any text around them, although the different search engines serve up their results in different ways, some better than others.
Its good for SH in that people find out about the site through many different search queries, but its worth remembering that its never wise to post anything on an open forum that you wouldn't want the rest of the world to see, as that is the way of the Internet.