当我没有在自定义字段中添加图片时，如何检索图片，比如说（没有图片）

我使用此代码检索字段。。。

<img class="film" 
     src="/scripts/timthumb.php?src=<?php the_field(\'img_actor\'); ?>&h=251&w=175&zc=1"
     alt="<?php the_title(); ?>"  
     title="<?php the_title(); ?>"/>

如何从此代码中检索无图片

<?php 
if(get_field(\'distributie\') != ""){$counter=0;foreach(get_field(\'distributie\') as $post_object): ?>
    <div class="act-box">
<a href="<?php echo get_permalink($post_object->ID); ?>" title="Actor <?php echo get_the_title($post_object->ID) ?>">
<img class="actor_img" src="/scripts/timthumb.php?src=<?php echo get_field( \'img_actor\', $post_object->ID ); ?>&h=70&w=50&zc=1" alt="<?php echo get_the_title($post_object->ID) ?>" title="<?php echo get_the_title($post_object->ID) ?>" /></a>
        <span class="act-titlu">
<a href="<?php echo get_permalink($post_object->ID); ?>" title="Actor <?php echo get_the_title($post_object->ID) ?>"><?php echo get_the_title($post_object->ID) ?></a>
        </span>
     </div>
<?php $counter++;if($counter>=8) break; endforeach;}?>

如果我改变

<?php echo get_field( \'img_actor\', $post_object->ID ); ?>

使用

<?php echo urlencode($img); ?>

我得到一个错误（$post\\u object->ID），我应该把它放在哪里？

<?php
if ( ! $img = get_field(\'img_actor\', get_the_ID() ) )
    $img = \'http://www.example.com/wp-content/uploads/default.jpg\';
?>
<img class="film" 
     src="/scripts/timthumb.php?src=<?php echo urlencode($img); ?>&h=251&w=175&zc=1"
     alt="<?php the_title_attribute(); ?>"  
     title="<?php the_title_attribute(); ?>"/>

 $attachments = get_children(
                             array(
                                   \'numberposts\' => 1,
                                   \'order\'=> \'ASC\',
                                   \'post_mime_type\' => \'image\',
                                   \'post_parent\' => get_the_ID(),
                                   \'post_status\' => null,
                                   \'post_type\' => \'attachment\'
                                   ));

        //first check for featured image
        if ( has_post_thumbnail() ) {

            the_post_thumbnail(\'thumbnail\');

        //no featured image get first attachment   
        } elseif ($attachments) { 

        $first_attachment = reset($attachments);
            echo wp_get_attachment_image($first_attachment->ID, \'thumbnail\');

        } else {
            echo \'<img src="../something/default.jpg"\'; 
        }