Drupal 7. Add apple-touch-icon.png in your theme folder I use 120x120 image size

drupal7_apple-touch-icon.php

<?php
function YOUR_THEME_NAME_preprocess_html(&$vars) {
    $apple = array(
      '#tag' => 'link',
      '#attributes' => array(
        'href' => base_path() . path_to_theme() .'/apple-touch-icon.png',
        'rel' => 'apple-touch-icon',
        'sizes' => '120x120'
      ),
    );
    drupal_add_html_head($apple, 'apple-touch-icon');
}
?>