Example of a block with custom theme.

EXAMPLE.module

<?php

/**
 * Implements hook_theme().
 */
function EXAMPLE_theme() {
  $path = drupal_get_path('module', 'EXAMPLE');
  $hooks = array(
    'iu_license' => array(
      'template' => 'iu-license',
      'path' => $path,
      'variables' => array(
        'copyright' => NULL,
        'license_text' => NULL,
        'license_link' => NULL,
        'license_image' => NULL
      ),
    ),
  );
  return $hooks;
}

/**
 * Implements hook_block_info().
 */
function EXAMPLE_block_info() {
  $blocks['copyright'] = array(
    'info' => t('Copyright'),
    'cache' => DRUPAL_CACHE_GLOBAL,
  );
  return $blocks;
}

/**
 * Implements hook_block_view().
 */
function EXAMPLE_block_view($delta) {
  $block = array();
  
  switch ($delta) {
    case 'copyright':
      $block['content'] = array(
        '#theme' => 'iu_license',
        '#copyright' => variable_get('site_name') . ' - ' . date('Y'),
        '#license_text' => 'licencia de Creative Commons Reconocimiento-NoComercial-CompartirIgual 4.0 Internacional',
        '#license_link' => 'http://creativecommons.org/licenses/by-nc-sa/4.0/deed.es_ES',
        '#license_image' => 'http://i.creativecommons.org/l/by-nc-sa/4.0/es/88x31.png',
      );
      break;
  }

  return $block;
}

iu-license.tpl.php

<div class="copyright"><?php print $copyright; ?></div>

<div class="license">
<?php
  $options = array('attributes' => array('rel' => 'license'));
  $image = theme('image', array(
    'path' => $license_image,
    'alt' => 'Licencia de Creative Commons',
    )
  );
  print l($image, $license_link, $options + array('html' => TRUE));
?>
<br/>
<?php print 'Esta obra está bajo una ' . l($license_text, $license_link, $options); ?>
</div>