With TypePad's template builder you can easily display custom content on your weblog. Additionally, Plus and Pro members have the ability to create custom template styles to change the columns, individual fonts and colors, and add a banner image.
Custom styles are configured on the Design > Style page for the template set. Using the Page Banner Element there, you can upload the image to use for your banner. Check the box to "Use this banner image instead of a text title" and use the image uploader to upload your banner image. Your banner should a .jpg, .gif, or .png file.
Before this, when creating your banner, you'll need to decide the size that you should use for the image.