Once you upload a header photo, that image is visible to others accessing your Twitter page via iPad, iPhone or Android apps as well as via Twitter.com.
To upload a header photo to your Twitter page, navigate to the gear icon in the top-right of your Twitter.com page and select “Edit profile.”
Then, from the menu on the left, click “Design” and scroll to the bottom. Under “Customize your own,” you’ll notice that your header defaults to a gray box. Here, you can upload your own image, but be sure that the minimum dimensions are 1252×626 and that it has a file size smaller than 5MB.
Your changes will appear instantly, but they’re not saved until you click “Save changes.”
In addition to the new profiles, photo streams now appear below your most recent tweets on iPhone, Android and iPad apps. To view them, swipe through the stream and tap the thumbnail to view them in full-screen.