Add HTML to Ubercart's checkout table I have a product with an attribute called ID. This ID is a reference to an image the user has uploaded, its filename is id.jpg.

In the cart table where it lists attributes it has "ID: 4" for example but can I throw an img tag in there with src '...4.jpg'?

I'm a fairly competent developer however I haven't done any module development. Thanks!
I just wrote a quick test of this hook and got what I think you're looking for...

Here is your chance to write your first module. If you're up on PHP, creating a module and enabling it is a 10 minute task. 

Once you have a module that your drupal installation recognizes as enabled, you're well on the way. I tested hook_cart_item and found the entire content of the cart... 

Note that there are several invocations of this hook, you'll want to inject your changes at the appropriate stage. 
In the example code below, I simply made a folder in sites/all/module/modcart
Then, created a module called modcard.module, (as wall as a modcard.info file). 

/**
  * Implementation of hook_cart_item()
 */
 function modcard_cart_item($op, &amp;$item) {
  global $user;
  $test = $op;
 }


Reference: http://www.ubercart.org/docs/api/hook_cart_item

Hope this helps.