When an image field displays an image with empty *alt* or *title* attributes, these get filled with the label of the corresponding entity. Using hook_preprocess_field() we target view mode displays but not Views using fields. hook_field_attach_view_alter() though targets everything. This code may play well in both a module and a theme.

imageprefillalttitle.php

<?php
/**
 * Implements hook_field_attach_view_alter().
 *
 * It fills the empty "alt" and "title" attributes of images with the label of
 * the corresponding entity.
 */
function mymodule_field_attach_view_alter(&$result, $context) {
  if (!empty($context['entity_type']) && !empty($context['entity'])) {
    $label = entity_label($context['entity_type'], $context['entity']);
    $fields = element_children($result);
    foreach ($fields as $field) {
      if ($result[$field]['#field_type'] == 'image') {
        $items = element_children($result[$field]);
        foreach ($items as $item) {
          if (isset($result[$field][$item]['#item'])) {
            if (empty($result[$field][$item]['#item']['alt'])) {
              $result[$field][$item]['#item']['alt'] = $label;
            }
            if (empty($result[$field][$item]['#item']['title'])) {
              $result[$field][$item]['#item']['title'] = $label;
            }
          }
        }
      }
    }
  }
}