Facebook has introduced Cover Photo which allows you to put any banner on your profile page, it looks good and nice, Then Google has also introduced cover photo concept for its Google+ social networking site.
Now Twitter has also introduce header image which allows you to upload and set any image as you header image on your profile. It will be shown top of your tweets on Twitter.com and all mobile apps.
The layout and placement of header image is same across all platforms but size will vary. Your image must have at least dimension of 1252×626 and can be of size up to 5 MB.
If you wanna set a header image then navigate to your twitter Setting page and then click on Design tab and upload your image or you can visit it directly from HERE.