Shortcode with custom image field?

Hi

I cannot get the image from one of my fields into a shortcode.
(it works with get_the_post_thumbnail($post->ID, ‘thumbnail’) But i need the value from the field “udstiller logo”

Here is my code

function logo_shortcode( $atts ) {
	extract( shortcode_atts( array(
		'limit' => '50',
		'orderby' => 'name',
	), $atts ) );
	// Creating custom query to fetch the project type custom post.
	$loop = new WP_Query(array('post_type' => 'udstillere', 'posts_per_page' => $limit, 'orderby' => $orderby));
	$output = '<ul class="bxslider">';
	// Looping through the posts and building the HTML structure.
	if($loop){
		while ($loop->have_posts()){
			 $loop->the_post();
			 $output .= '<li><a href="'.get_permalink().'"><img src="'.get_post_meta($post->ID,'wpcf-udstiller-logo',true).'"/></a></li>';

		}
	}
	else
		$output = 'Sorry, No projects yet. Come back Soon.';
	// Now we are returning the HTML code back to the place from where the shortcode was called.
	return $output;
	$output = '</ul>';
}
add_shortcode("Logo", "logo_shortcode");

https://www.ads-software.com/extend/plugins/types/