Ok,
I've changed
<?php if ($url) : ?>
<a class="uk-align-<?php echo $image_alignment; ?>" href="<?php echo $url; ?>" title="<?php echo $image_caption; ?>"><img src="<?php echo $image; ?>" alt="<?php echo $image_alt; ?>"></a>

in
<?php if ($url) : ?>
<img class="uk-align-<?php echo $image_alignment; ?>" src="<?php echo $image; ?>" alt="<?php echo $image_alt; ?>">

Problem solved.