Google recently announced it was switching Gmail to automatically display external images instead of making the user click a button to do so. This means that email marketers will be able to see when you open an email - they frequently put tracking images in emails. Google is also moving to having its servers get these images for you, so that Google can scan them for known malware and hide your IP from the email marketers.

Be sure to go back into your Gmail settings today and set the External Content setting to Ask before displaying external content if this is important to you.

http://arstechnica.com/security/2013...ght-and-today/