Make image style links not focusable (fe. when there are other read more links already available)

template.php

<?php

/* 
 *  Implements hook_preprocess_image_formatter() to add tabindex to teaser img links
 */
function theme_preprocess_image_formatter(&$vars) {
  if ($vars['image_style'] == "yourimagestyle") {
    if(!empty($vars['path'])) {
      $vars['path']['options']["attributes"]["tabindex"] = -1;
    }
  }
}