insert thumbnail image from php script

Question

I'm trying to insert a post image thumbnail from my php scritp. It's inserting the post, the content, a download link, and I only need to set the thumbnail image to finish my script. This is my code but I can't figure out why is not working, anyhelp would be appreciated:

    $url = "http://www.test.com/wp-content/uploads/2015/12/".$title[$key1].".png";

$attr = array(
'src'   => basename($url),
'class' => "alignleft",
'alt'   => '',
'title' => trim( strip_tags( 'Logo' ) )
);
the_post_thumbnail('thumbnail', $attr );

Answer 1

You'll want to take a look at wp_insert_attachment and wp_generate_attachment_metadata.

You can't insert a featured image/thumbnail using the_post_thumbnail - that function only gets the thumbnail for the current post.

See: http://codex.wordpress.org/Function_Reference/wp_insert_attachment and http://codex.wordpress.org/Function_Reference/wp_generate_attachment_metadata

Answer 2

To set a thumbnail for a post you should upload the file to your server. Use the below function to upload the file from URL:

function upload_file($image_url, $post_id)
{
    $image = $image_url;

    $get = wp_remote_get($image);

    $type = wp_remote_retrieve_header($get, 'content-type');

    if (!$type) {
        return false;
    }

    $mirror = wp_upload_bits(basename($image), '', wp_remote_retrieve_body($get));

    $attachment = array(
        'post_title' => basename($image),
        'post_mime_type' => $type
    );

    $attach_id = wp_insert_attachment($attachment, $mirror['file'], $post_id);

    require_once(ABSPATH . 'wp-admin/includes/image.php');

    $attach_data = wp_generate_attachment_metadata($attach_id, $mirror['file']);

    wp_update_attachment_metadata($attach_id, $attach_data);

    return $attach_id;
}

Then run the function:

$url = 'http://yoursite.com/photo.jpg';
$post_id = 56;

upload_file($url, $post_id);