1) Open the page catalog xml and search the for the string “catalog/product/list.phtml’

2) Include the code
<action method=”addAttribute”><name>alternate_another_imageimage</name></action>
after
<block type=”catalog/product_list” name=”product_list” template=”catalog/product/list.phtml”>

3) Call the below given code on list.phtml

$another_image = $this->helper(‘catalog/image’)->init($_product, another_image)->resize(135); // Assuming another_image is the attribute code