Display featured image as post thumbnail

Question

i'm trying to set up a mobile theme for my WordPress site. My desktop version uses themejunkie's weekly theme and my mobile version uses dotmobi theme.

the Dotmobi theme pulls out the first image and displays as a thumbnail where as the weekly theme displays the 'featured image' as a thumbnail or a picture that is defined in a custom field value 'thumb'

How can I make use of this same logic for dotmobi as well?

I tried get_thumbnail() but that doesn't work. Any help on this please.

I also tried by putting this code into my functions.php

// Get image attachment (sizes: thumbnail, medium, full)
function get_thumbnail($postid=0, $size='full') {
    if ($postid<1) 
    $postid = get_the_ID();
    $thumb_key = get_theme_mod('thumb_key');
    if($thumb_key)
        $thumb_key = $thumb_key;
    else
        $thumb_key = 'thumb';
    $thumb = get_post_meta($postid, $thumb_key, TRUE); // Declare the custom field for the image
    if ($thumb != null or $thumb != '') {
        return $thumb; 
    } elseif ($images = get_children(array(
        'post_parent' => $postid,
        'post_type' => 'attachment',
        'numberposts' => '1',
        'post_mime_type' => 'image', ))) {
        foreach($images as $image) {
            $thumbnail=wp_get_attachment_image_src($image->ID, $size);
            return $thumbnail[0]; 
        }
    } else {
        return get_bloginfo ( 'stylesheet_directory' ).'/images/default_thumb.gif';
    }

}

and called the same in my index.php through

<?php echo '<a href="'.get_permalink($post->ID).'" rel="bookmark"><img src="'.get_bloginfo('template_url').'/timthumb.php?src='.get_thumbnail($post->ID, 'full').'&amp;h='.$height.'&amp;w='.$width.'&amp;zc=1" alt="'.get_the_title().'" /></a>' ?>

For some odd reason the thumbnails aren't displaying

Answer 1

Try this code.

Then temporarily set permissions to the cache folder to 774 and the timthumb.php file to 750, you can increase or decrease the permissions as you see fit (or aslong as it stops working, then it'll be time to loosen up the permissions).

<?php
    // If there are images get them
    if ( $images = get_children(array(
        'post_type' => 'attachment',
        'numberposts' => 1,
        'post_status' => null,
        'post_parent' => $post->ID
    )));

    foreach( $images as $image ) {
         $attachment = wp_get_attachment_image_src( $image->ID );

    // Variables for timthumb
    $width = 160;
    $height = 160;
    $zoom_crop = 1;
?>

<a href="<?php the_permalink() ?>" rel="bookmark" title="<?php esc_attr( printf( __( 'Click to read %s', 'truereps' ), get_the_title() ) ); ?>">
<img src="<?php bloginfo( 'template_directory' ); ?>/inc/scripts/timthumb.php?src=<?php echo $attachment[0]; ?>&amp;w=<?php echo $width; ?>&amp;h=<?php echo $height; ?>&amp;zc=<?php echo $zoom_crop; ?>" alt="<?php the_title(); ?>" />
</a>

<?php } ?>