Relative path to images in blog-directory plugin.

I want to be able to show some images on the blog directory list. (Fancy buttons, graphics etc.)
I can display them by using the full pathname (http://www.myDomain/images/image.jpg.) However, I would like to be able to put the images in a folder in the mu-plugins and display them from there relative to the blog-directory.php file in my WPMU installation.

The code I have is as follows:
// content=.'<img src = "target="_blank" href="http://www.myDomain.com/wp-content/mu-plugins/images/myDesiredImage.jpg " >' ; //

How can I make a relative path to display myDesiredImage.jpg on the blogs-directory.php file.
Hopefully displaying images on my blog list without going around the world!!

Many thanks

Ray