$images = rwmb_meta( 'field-id', array( 'size' => 'image-size', 'limit' => 1 ) );
$image = reset( $images );
echo $image['url'];
$images = rwmb_meta( 'field-id', array( 'size' => 'image-size', 'limit' => 1 ) );
$image = reset( $images );
echo $image['url'];