Following in the footsteps of Google+ and Facebook, Twitter last month turned on the ability to add what it calls a “header photo” to your profile.
This is different from your profile image, which is more of an icon; the header photo is a background image.
Header photo’s are viewable to visitors to your timeline who use iPad, iPhone and Android apps, as well as through the main twitter.com website.
Adding your header photo is easy; just navigate to the gear icon at the top right of the page and click on “Edit Profile”.
From there, click “Design” in the menu on the left. About half way down the page you will see a section titled “Customize your own”.
Upload your image, making sure that the minimum dimensions are 1252x626px and that the file size is less than 5MB, and remember to hit save at the bottom of the page for your changes to take effect!