Some themes allow you to customize the image used on the blog’s header. Here’s an example of a custom image header:
To select a custom image, first login to WordPress and go to your site’s Dashboard.
Under Appearance select Custom Image Header.
You’ll see a screen with your current header image and will have the option to select either change some characteristics of the current image (hide text, select text color, use original color) or you can upload a new header image (click this thumbnail image to see a larger image).
To choose an image from your computer, click Browse.
Locate the file on your computer and click Open.
The image file name will be entered in the Choose an image from your computer: text box. Click the Upload button.
The image header preview will open. On this screen select the part of the image you want to use as your header. (Click this thumbnail image to see larger image.)
When finished, click the Crop Header button at the bottom of the image preview.
A confirmation message will appear tell you that the header is complete.
Visit your site to see the new header image.