Correct way of using wp_get_attachment_image() in wordpress

Question

I'm looking for the correct way of using wp_get_attachment_image().

The following code:

<?php
    $args = array(
        'type' => 'attachment',
        'category_name' => 'portfolio'
        );
    $attachments = get_posts($args);
    print_r($attachments);
?>

Generates the following result:

Array
(
    [0] => stdClass Object
        (
            [ID] => 54
            [post_author] => 1
            [post_date] => 2010-06-22 00:32:46
            [post_date_gmt] => 2010-06-22 00:32:46
            [post_content] => <a href="http://localhost/wordpress/wp-content/uploads/2010/06/Capture.jpg"><img class="alignnone size-medium wp-image-55" title="Capture" src="http://localhost/wordpress/wp-content/uploads/2010/06/Capture-300x114.jpg" alt="" width="300" height="114" /></a> 
            [post_title] => Our Own Site
            [post_excerpt] => 
            [post_status] => publish
            [comment_status] => open
            [ping_status] => open
            [post_password] => 
            [post_name] => our-own-site
            [to_ping] => 
            [pinged] => 
            [post_modified] => 2010-06-22 00:40:22
            [post_modified_gmt] => 2010-06-22 00:40:22
            [post_content_filtered] => 
            [post_parent] => 0
            [guid] => http://localhost/wordpress/?p=54
            [menu_order] => 0
            [post_type] => post
            [post_mime_type] => 
            [comment_count] => 0
            [filter] => raw
        )
)

The following, however, doesn't return anything.

<?php
    echo wp_get_attachment_image(54, array('300', '300'));
?>

What am I doing wrong here?

Answer 1

Actually, I don't think the accepted answer really answers the question.

Your problem is that you're passing in the post id (54 in your example; typically $post->ID in WP parlance) to wp_get_attachment_image(). As can be seen in the codex, you're supposed to use the attachment id (see $attachment_id below):

wp_get_attachment_image( $attachment_id, $size, $icon );

In other words, you've got to do something like this:

$image_attr = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID), 'medium');

Answer 2

wp_get_attachment_image function can accept four values as you can see:

wp_get_attachment_image ( int $attachment_id, string|array $size = 'thumbnail', bool $icon = false, string|array $attr = '' )

So i always use:

<?php echo wp_get_attachment_image( get_the_ID(), array('700', '600'), "", array( "class" => "img-responsive" ) );  ?>

Note: we can simply use get_the_ID() to pass id of active post. and here 700 is width and 600 is height of attachment image. we can also pass our class as array( "class" => "img-responsive" )