you dont need to edit the display manager, just the code on the cart page.
In design view, select the thumbnail image in the cart.
In the property inspector, click the lightning bolt next to source, and select the image column from your cart. This will create code similar to:
php:
<img src="<?php echo $YourCartName->DisplayInfo("Thumb"); ?>" alt="" />
where YourCartName is the name of your cart object.
you will need to prepend the image path in front of this:
php:
<img src="images/path/<?php echo $YourCartName->DisplayInfo("Thumb"); ?>" alt="" />
