Gmail will automatically display images that are embedded in emails. Previously, Gmail always prompts if you want to "display images below" to safeguard against unknown senders who might attempt to use images to compromise the security of your PC or mobile device.
Now, all images will be laid out in your messages by default, across desktop, iOS, and Android, thanks to enhancements in how Gmail handles visuals. Your images will be checked for malicious content such as known viruses and malware, so you'll never have to select the "display images below" option again. Instead of serving images directly from their original external host servers, Gmail will now serve all images through Google’s own secure proxy servers.
Of course, those who prefer to authorize image display on a per message basis can choose the option “Ask before displaying external images” under the General tab in Settings. That option will also be the default for users who previously selected “Ask before displaying external content”.
Similar to existing features like default https access, suspicious activity detection, and free two-step verification, image proxying is another way your email is protected. This new improvement will be rolling out on desktop starting today and to your Gmail mobile apps in early 2014.
Source: Official Gmail Blog
Images accredited to Google.