Do you have a "favicon" in mind -the icon that appears left of the page's name in the browser tab? If so, just add a small .ico or .png picture in your graphics folder and include this in your study HTML <head> Tag.
<link rel="shortcut icon" href="[% GraphicsPath() %]favicon.png">
Just in case, Google provide a nice trick to capture the favicon of any site (e.g. your client's site):
If you mean adding another picture on top of the favicon, I would not know how.