As per shopify it does not allow us to modify their checkout page fully (Partial modification for shopify Plus merchant). We cannot change any liquid code of line item in their checkout. So the only way to show personalized image in checkout is creating new product. Here is how to do that in the app .

This way each time customer  hit add to cart button there will be a new product creation with personalized image as featured image thus it will be shown in checkout page also. You need to delete these newly created product after fulfillment .

Hide newly Created product from collection and search result

Or

Delete newly created product automatically after certain time.