You can add a field to whatever document type that you are using and have it as a url selector which points to an image and then include some code such as this:
<style>
.top-title-img{
background: url('http://mydomain.com<%= CMS.MacroEngine.MacroContext.CurrentResolver.ResolveMacros("{%CurrentDocument.GetValue(\"myfieldname\")|(identity)GlobalAdministrator%}") %>') scroll center no-repeat;
}
</style>