Memory limit proof generate CSV of missing product images

gistfile1.php

<?php

// generate a CSV of id,sku of products with missing images to var/missingimages.csv
// core/resource_iterator used to prevent memory max limits issues
// original source: https://stackoverflow.com/questions/3565377/how-can-i-find-all-products-without-images-in-magento

require_once('app/Mage.php');
umask(0);
ini_set('display_errors', 1);
Mage::setIsDeveloperMode(true);
Mage::app();
set_time_limit(0);
Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);

function productCallback($args)
{
    $product = Mage::getModel('catalog/product');
    $product->setData($args['row']);
    echo $product->getSku() . "\n<br />";
    $product_data = array();
    $product_data['id'] = $product->getEntityId();
    $product_data['sku'] = $product->getSku();
    $GLOBALS['csvdata'][] = $product_data;
}

$products = Mage::getModel('catalog/product')
    ->getCollection()
    ->addAttributeToSelect('sku')
    ->addAttributeToFilter(array(
        array (
            'attribute' => 'image',
            'like' => 'no_selection'
        ),
        array (
            'attribute' => 'image', // null fields
            'null' => true
        ),
        array (
            'attribute' => 'image', // empty, but not null
            'eq' => ''
        ),
        array (
            'attribute' => 'image', // check for information that doesn't conform to Magento's formatting
            'nlike' => '%/%/%'
        ),
    ));

Mage::getSingleton('core/resource_iterator')->walk($products->getSelect(), array('productCallback'), array('arg1' => '===='));

$file = 'var/missingimages.csv';
$csv = new Varien_File_Csv();
$csv->setDelimiter(',');
$csv->setEnclosure('"');
$csv->saveData($file, $csvdata);