How would I change default image from the small to the medium or large

Hi there, this is not an image size management question - I understand the sizing, etc...
I use 3 completely different images for the main product image in a cart I am setting up.
I am afraid I am stuck on this silly little "simple" thing.:frusty:

I need the image that displays on the product page and details page to be one image - the (medium) photo that the person would order to be placed on the product and then the image that ends up in the shopping cart to be a second image - the small photo I have merged with the product so that they and the store owner see a preview what they are getting.
I went around and around yesterday trying to accomplish this through the back end and couldn't.

I can't figure out how to edit either the shopping cart templates to use the medium image.Alternately i would have to modify several of the product pages which again - not sure how to change. None of my blind guesses worked.
Then I thought that I could simply define the default image as the medium image, but was unable to find where I might do that. Can any of you point me in the right directions or suggest what I might do? I have been staring at it too long and it seems like it should be a very simple task. I must have missed something.

I do have image handler installed and 1.51 and i am currently playing with stirling_grand responsive template. It's not up yet so can't provide a link, sorry.

Thanks in advance.

this is what I thought I could edit, but I don't htink that will work unless I do after Iadd all of the products```

<?php /** * main_product_image module * * @package templateSystem * @copyright Copyright 2003-2006 Zen Cart Development Team * @copyright Portions Copyright 2003 osCommerce * @license http://www.zen-cart.com/license/2_0.txt GNU Public License V2.0 * @version $Id: main_product_image.php 4663 2006-10-02 04:08:32Z drbyte $ */ if (!defined('IS_ADMIN_FLAG')) { die('Illegal Access'); } $products_image_extension = substr($products_image, strrpos($products_image, '.')); $products_image_base = str_replace($products_image_extension, '', $products_image); $products_image_medium = $products_image_base . IMAGE_SUFFIX_MEDIUM . $products_image_extension; $products_image_large = $products_image_base . IMAGE_SUFFIX_LARGE . $products_image_extension; // check for a medium image else use small if (!file_exists(DIR_WS_IMAGES . 'medium/' . $products_image_medium)) { $products_image_medium = DIR_WS_IMAGES . $products_image; } else { $products_image_medium = DIR_WS_IMAGES . 'medium/' . $products_image_medium; } // check for a large image else use medium else use small if (!file_exists(DIR_WS_IMAGES . 'large/' . $products_image_large)) { if (!file_exists(DIR_WS_IMAGES . 'medium/' . $products_image_medium)) { $products_image_large = DIR_WS_IMAGES . $products_image; } else { $products_image_large = DIR_WS_IMAGES . 'medium/' . $products_image_medium; } } else { $products_image_large = DIR_WS_IMAGES . 'large/' . $products_image_large; } /* echo 'Base ' . $products_image_base . ' - ' . $products_image_extension . '<br>' . 'Medium ' . $products_image_medium . '<br><br>' . 'Large ' . $products_image_large . '<br><br>'; */ // to be built into a single variable string ?>

You said you want the main product image as shown on the product-details page to be the medium image. Good. That's what Zen Cart does normally out-of-the-box.
Everywhere else it uses the smaller thumbnail image.

I need the "small" image that is sent to the cart to be different from the image shown everywhere else, so want to use it only as the image to go through to the cart. thought that I could simply change the cart page and switch the line to ['products_image_medium'] but that didn't work. not sure why.

  </td>
       <td class="cartProductDisplay">
<a href="<?php echo $product['linkProductsName']; ?>"><span id="cartImage" class="back"><?php echo $product['products_image']; ?></span><span id="cartProdTitle"><?php echo $product['productsName'] . '<span class="alert bold">' . $product['flagStockCheck'] . '</span>'; ?></span></a>
<br class="clearBoth" />

I am sorry - very confusing and hard to explain. the small and medium images in my case are the same size. The medium image that displays on the product details page is a preview of the merged product which is fine, but I want either to send that medium image to the cart, or to change the image that displays everywhere else to be the medium image. Does that make sense?

Think I got it by editing the modules/product_listing.php as follows. Still checking to see that it does not break anything else. Seems to work. suppose I will have to reapeat other places as well

            $lc_text = '<a href="' . zen_href_link(zen_get_info_page($listing->fields['products_id']), 'cPath=' . (($_GET['manufacturers_id'] > 0 and $_GET['filter_id']) > 0 ?  zen_get_generated_category_path_rev($_GET['filter_id']) : ($_GET['cPath'] > 0 ? zen_get_generated_category_path_rev($_GET['cPath']) : zen_get_generated_category_path_rev($listing->fields['master_categories_id']))) . '&products_id=' . $listing->fields['products_id']) . '">' . zen_image(DIR_WS_IMAGES . 'medium/' . $listing->fields['products_image'], $listing->fields['products_name'], IMAGE_PRODUCT_LISTING_WIDTH, IMAGE_PRODUCT_LISTING_HEIGHT, 'class="box_image"') . '</a>';
          }
        }

EEEEEEEK ! whatever I did, don't do it. I broke the template. :-( can't get past 3 products in a category and all of the images go away. renamed, retried 100 times, deleted categories, retried with different names, Not sure what happened. It seemed to work great until I tried to populate the products. Ugh.

Don't do what I did, maybe Dr. Byte should delete this?

http://www.zen-cart.com/content.php?124-blank-page

lol, well not 'til later.
It worked I think until I uploaded an image this am to test ih- oops forgot and left it like that- I think that it worked becuase I had emptied the _MED directory setting in the back end to see what would happen, so it worked because it was having an error and displaying the LRG image instead...I think. Actually it worked just the way I wanted except for the file sizes and duplicated folders I encountered. I didn't intend to upload with it like that.
I am trying to duplicate a site for a friend that creates a product with a on-the-fly pasted on image from a choice of a few hundred photos. It then sends this picture to the owner who creates and ships it. I can't do such a thing. It's way beyond even playing with. I can not figure out how to get the photo that is to be selected as the main photo, but have the email send the "merged" image. I am just playing with it, though - not live and won't be if I can't figure out how to go about that. I think I have to maybe make an extra database table, but was trying to get around it. It just seems like such a simple thing and sometimes I start off in the wrong direction and can't get straightened out. Thanks.