<?php

       $array = array(
           'item-img-list' => array(
              array(
                 'image-type' => 1,
                 'image-url' => 'http://i...content-available-to-author-only...g.pl/...'
              ),
              array(
                 'image-type' => 2,
                 'image-url' => 'http://i...content-available-to-author-only...g.pl/...'
              ),
              array(
                 'image-type' => 3,
                 'image-url' => 'http://i...content-available-to-author-only...g.pl/...'
              )
           )
        );
        $newArray = array();

        foreach($array['item-img-list'] as $k=>$v){
          $newArray[$v['image-type']] = $v['image-url'];
        }
        print_r($newArray);