Twitter announced an update to its app and site design yesterday.
The update auto populates your timeline with photos and Vine videos. Before, you had to click through the tweet to see the media that was being shared.
It takes up a lot of "screen real estate" so if this isn't your cup of tea, here's the simple two-step way to turn it off.
First go into your settings:
Then, swipe back on "Image Preview". (Green means on, no green means off.)