admin-column-callback-image.php

/**
 * Show image by stored image ID
 *
 * $meta_key - custom field to get image from
 * $size     - image size to show
 */
function jet_admin_column_date( $column, $post_id ) {

	$meta_key = '_image';
	$image_id = get_post_meta( $post_id, $meta_key, true );
	$size     = 'thumbnail';

	if ( ! $image_id ) {
		return '--';
	} else {
		return wp_get_attachment_image( $image_id, $size );
	}

}