How to get Image `alt` value from WordPress image attachment?

This looks like how you should use WCK:

<?php
foreach( get_cfc_meta( 'testimonialsbox' ) as $key => $value ){ ?>
    <?php $author_testimonial = $key['author_testimonial']; ?>
    <?php $photo_obj = get_cfc_field( 'testimonialsbox','photo', false, $key );  ?>
    <div class="col-md-6 col-sm-6">
        <?php echo $author_testimonial; ?>
        <div class="author-det">
            <img src="https://wordpress.stackexchange.com/questions/279399/<?php echo $photo_obj["url'] ?>" alt="https://wordpress.stackexchange.com/questions/279399/<?php echo $photo_obj["alt']; ?>"/>
        </div>
    </div>
<?php } ?>