index.php
....
....
global $used_img;
	$used_img[1]=0;
    while ($categories = tep_db_fetch_array($categories_query)) {
      $rows++;
      $cPath_new = tep_get_path($categories['categories_id']);
      $width = (int)(100 / $MAX_DISPLAY_CATEGORIES_PER_ROW) . '%';
      $used_imgs=implode(',',$used_img);
      $image = get_random_cat_image($categories['categories_id'],0,$used_imgs);
      array_push($used_img, '"' . $image . '"');
echo '                <td align="center" class="smallText" width="' . $width . '" valign="top"><a href="' . tep_href_link(FILENAME_DEFAULT, $cPath_new) . '">' . tep_image(DIR_WS_IMAGES . $image, $categories['categories_name'], SMALL_IMAGE_WIDTH, SMALL_IMAGE_HEIGHT) . '<br>' . $categories['categories_name'] . '</a></td>' . "\n";
      if ((($rows / $MAX_DISPLAY_CATEGORIES_PER_ROW) == floor($rows / $MAX_DISPLAY_CATEGORIES_PER_ROW)) && ($rows != $number_of_categories)) {
        echo '              </tr>' . "\n";
        echo '              <tr>' . "\n";
      }
    }
....
....

random_cat_images.php

define('EMPTY_CAT_IMAGE', 'empty.gif');

function get_random_cat_image($category_id, $count = 0, $used_imgs)
{
	srand ((double)microtime()*1000000);
	$retun_val;
	if($category_id > 0 && tep_count_products_in_category_without_sub($category_id) > 0 && $count < 10)
	{
		
		$randInt = rand(1,10);
		$randStart = $randInt -1;
 $produkt_query = tep_db_query(	"select distinct p.products_image as img ".
   		"from products p, " . TABLE_PRODUCTS_DESCRIPTION . " pd, " . TABLE_PRODUCTS_TO_CATEGORIES . " p2c, " . TABLE_CATEGORIES . " c ".
   		"where p.products_id = pd.products_id and p.products_id = p2c.products_id and ".
   		"p2c.categories_id = c.categories_id and '" . $category_id . "' in (c.categories_id, c.parent_id) and ".
   		"p.products_image = p.products_image not in (" . $used_imgs . ")".
   		" order by pd.products_viewed desc limit 3"); 				
						
		while($result = tep_db_fetch_array($produkt_query))
		{
			
			$retun_val = $result['img'];
			if(rand(1,10) > 9)
				break;
		}
				
		if(!(tep_not_null($retun_val)) &&  tep_has_category_subcategories($category_id))
		{
			$retun_val = get_random_cat_image_from_child($category_id,$count,$used_imgs);
		}
		
	}
	else if($category_id > 0 && tep_has_category_subcategories($category_id) && $count < 10)
	{
		
		$retun_val = get_random_cat_image_from_child($category_id,$count,$used_imgs);
	}
	else
	{
		$retun_val = EMPTY_CAT_IMAGE;
	}
	
	
	return $retun_val;
	
}

function get_random_cat_image_from_child($category_id,$count = 0)
{
	$retun_val;
	$category_query = tep_db_query("select categories_id as ID from ". TABLE_CATEGORIES ." WHERE parent_id = ". $category_id ." LIMIT 0,". rand(1,10) );
	while($ids = tep_db_fetch_array($category_query))
	{	
		$id = $ids['ID'];
		
		$retun_val = get_random_cat_image($id, $count++, $used_imgs);
		if((tep_not_null($retun_val)) && $retun_val != EMPTY_CAT_IMAGE)
			break;
	}
	
	return $retun_val;
}

//Changed from osCommerce
  function tep_count_products_in_category_without_sub($category_id, $include_inactive = false) 
  {
    $products_count = 0;
    if ($include_inactive == true) {
      $products_query = tep_db_query("select count(*) as total from " . TABLE_PRODUCTS . " p, " . TABLE_PRODUCTS_TO_CATEGORIES . " p2c where p.products_id = p2c.products_id and p2c.categories_id = '" . (int)$category_id . "'");
    } else {
      $products_query = tep_db_query("select count(*) as total from " . TABLE_PRODUCTS . " p, " . TABLE_PRODUCTS_TO_CATEGORIES . " p2c where p.products_id = p2c.products_id and p.products_status = '1' and p2c.categories_id = '" . (int)$category_id . "'");
    }
    $products = tep_db_fetch_array($products_query);
    return $products['total'];
}
    
?>

*************************************
The problem:

Cuando index.php llama a la funtion get_random_cat_image() me devuelve valores duplicados. Hay algunos productos que se repiten en varias categorias pero yo le he implementado a mi manera como puedes ver un array en el cual se van introduciendo los valores ya tomados. Pero aun asi me duplica algunos.