Hide Alt and Title for image field

Here a solution for hide the alt and title fields:

/**
 * Implements hook_field_widget_form_alter().
 */
function MYMODULE_field_widget_form_alter(&$element, &$form_state, $context) {
    // If this is an image field type
    if ('image' === $context['field']['type'] && 'MY_FIELD' === $context['instance']['bundle']) {
    // Loop through the element children (there will always be at least one).
    foreach (element_children($element) as $key => $child) {
        // Add the new process function to the element
        $element[$key]['#process'][] = 'MYMODULE_image_field_widget_process';
    }
    }
}

function MYMODULE_image_field_widget_process($element, &$form_state, $form) {
    $element['title']['#access'] = FALSE;
    $element['alt']['#access'] = FALSE;

    // Return the altered element
    return $element;
}

Et voila :)

This could work with Field Permissions module...