Submit handler for overriding a module-defined style.
function image_style_form_override_submit($form, &$form_state) {
drupal_set_message(t('The %style style has been overridden, allowing you to change its settings.', array(
'%style' => $form_state['image_style']['label'],
)));
image_default_style_save($form_state['image_style']);
}