Hi,
As I can see, you transform one letter into one product in the cart, what is the custom field information for ?
To specify the code of the image used ?
If it is, so as you said you have to create a custom field in the product table, then when adding a product to the cart, populate the database column with the custom field name with the desired value. Then edit the view "checkout / cart" and for each product display the value of the custom field, you can use code to display an image directly in the cart.
www.hikashop.com/support/support/documen...ize-the-display.html