The image name for the product should be added to the cart using the add to cart button.
On the cart page, you should be getting the image name from the cart.
If it is showing the same image for each item in the cart, there 2 most likely causes:
1) In the Add to cart button, you have it set to look up the item ID from a recordset, the image column is bound to a differant recordset.
2) On the cart display page, you are retrieving the image name from a recordset rather than the cart.