By Kurt Wagner at Mashable:
Twitter streams across America are now full of pictures, but yours doesn't have to be.
An update to the microblogging site Tuesday automatically displays images and Vine videos meaning users don't need to click on a tweet in order to see its visual content. The change has already been implemented on the web, and is available to iOS and Android mobile users who update their app.
But not everyone wants to see tweeted pictures automatically, and there are ways to turn off Tuesday's new feature on mobile. Simply go to settings within the app, and deselect the "Image Previews" tab. Simple as that.
It does not appear that you can turn off picture and video previews on Twitter's desktop version, but there may be another setting you wish to visit. Open the settings tab on Twitter.com and you can find a way to set up warnings for content that might be sensitive. You can choose to be alerted when media that has been labeled as "Sensitive" comes across your feed.