First you need to add the image column to your eCart object.
Next you need to modify the add to cart buttons to store the image name for the product in the new image column, on the bindings tab of the add to cart button interface, select the image column, then click the lighting bolt next to value and select the image column from your recordset.
Finally, you need to add the image tag in the cart display:
<img src="imagesupload/<?php echo $WA_Store_Cart->DisplayInfo("Thumb"); ?>" alt="" />
this example assumes that the images are stored in the imagesupload directory, that the cart is named WA_Store_Cart and the image column is named Thumb. You need to make any needed corrections.