try something like this:
<ul class="slider">
<?php if( get_field('display_in_carousel') )
{
$image = get_field('image');
if( !empty($image) ): ?>
<li><img src="<?php echo $image['url']; ?>" alt="<?php echo $image['alt']; ?>" /></li>
<?php endif;
}
else
{
//do nothing
}
?>
</ul>
of course you need to wrap that like your slider need it (and probably change way of load image too)
or you do it with meta-query like the other part of the example
