Replace Text Link with Image
 

On the product page can someone tell me how i change the text Ask Question to Contact us or how i would replace it with a button (like add to cart) or just an image ?

the code is

{include file="customer/buttons/button.tpl" button_title=$lng.lbl_ask_question_about_product style="link" href="javascript: return !popupOpen(xcart_web_dir + '/popup_ask.php?productid=`$product.productid`')"}

i have tried adding an image with the link "javascript: return !popupOpen(xcart_web_dir + '/popup_ask.php?productid=`$product.productid`')" but it didnt work

would appreciate any help