enigma1 - 2:48 pm on Jan 10, 2012 (gmt 0)
They're testing many more things as far I understand from my server logs. Information they gather could be used to determine whether the site cloaks content, how fast the server responds on side resources, also to use instant preview, etc.
What is your concern if they access images setting up referrers? If it's image stealing you care about, you could watermark your images and let it have them.