Google has announced that they will show images by default now. This change will be rolled out to Gmail for Android and iOS in early 2014 as well. As of right now, Gmail will ask you if you want to show images in e-mail. They do this to protect users in case there is malware involved in the e-mail.
Google is making the changes so that images are served through their secure proxy servers instead of the original external host servers.
If you are concerned about these changes, you can turn images off again by going to the General tab under Settings and selecting ?Ask before displaying external images.?
[Source: Gmail Blog]