How to do this in vBulletin ?

[Rapid4All]

as Username HTML Markup. But then I only see the Image and Not the Username.

You should check your Html code which you added , if you add a long HTML code (url of image ...), your html code will not have close tag . Thats reason you just see image only. Make sure that your html code is closed.

"Username HTML Markup" R4A setting:
First BOX:

<b><font color="#3d89ae"><img src="a short url" border="0"/>

Second:

</font></b>