As per Shopify, we cannot fully modify their checkout page (Partial modification for Shopify Plus merchants) or change any liquid code of a line item in their checkout. So, the only way to show a personalized image in the checkout is by creating a new product. You can find the option in the General Settings section of the Customizer page.

This way, each time a customer hits the add-to-cart button, a new product will be created with the personalized image as the featured image; thus, it will be shown on the checkout page as well. You need to delete these newly created products after fulfillment.

Documentation to hide the newly created products in the collection and search page: Click here

Documentation to automatically delete the newly created products after certain time: Click here