Add a header above blog posts but below page header

Add a header above blog posts but below page header

How do I add an image to my blog page. I want it to appear under the page header but before the blog posts. It will be a static image (masthead for the blog). This is the address for the page: http://ganleyautoadvisors.com/blog/
I am using the Adada theme. I want the image to be as wide as the content area, the side bar stays.
Help!