You probably see that "Display images below" button in Gmail all the time on both mobile and desktop. This is the default behavior because it makes it harder for spammers and advertisers to track you. However, Google says it has prepared a workaround that mitigates the security concern and will allow it to show those images by default.

Images

When you get an email containing images, the files are loaded from an external host server. Each time you download the images in an email, the sender (read: spammer) can use that to track you. They know firstly that you are a real person and not a broken inbox, but it can also give them an IP address. Google is circumventing this by opening each image in the email, then serving it to you from its proxy servers instead of an external one. This instantly renders image loading data useless to spammers, and makes it safe to show you all your email pics by default.

Google is also going to be scanning for malicious content hidden in images at the same time. So consider this a double win. If you don't like awesome things, you can set Gmail to go back to the old behavior of hiding images by default.

[Gmail Blog, +Gmail]