This is what worked for me. Based on @hube2 but cleaned up a bit. Thanks!
<a href="<?php the_sub_field('link', 'option'); ?>" target="_blank">
<img class="test" src="<?php the_sub_field('image'); ?>" alt="<?php
echo get_post_meta(get_sub_field('image', false), '_wp_attachment_image_alt', true); ?>">
</a>
