I know this is a bit old, but I just searched it myself. The answer I used was Ashwini Verma's, but I don't know if the answer is clear enough, or maybe I went beyond what was intended, so...
I had a need for several image buttons providing a CommandName. However, I also needed to have text on the buttons, and I didn't really want to make new images with the current image and the text. This is how I solved the problem using a LinkButton as my "Refresh":
<asp:Linkbutton ID="Something" runat="server" CommandName="Refresh" Text="<div class='topbutton'><div align='center'><img height='21px' width='21px' src='imagepath/toggle.png' alt='Refresh'/></div>Refresh</div>"></asp:LinkButton>
I'm a new member to the site and cannot yet post images of the button, but I hope you get the idea.