Display image from ACF gallery only if it has meta field - php

Question

I have an ACF image gallery and have set up a True / False (1/0) custom field to image attachments named "featured_image". Inside the gallery, several images are selected as the featured image while others are not.
What I would like to achieve is to randomly select one of the images which has the "featured_image" custom field as true.
My code thus far is included below, however I cannot get it to work by selecting only images from the gallery marked as "featured_image", or know how to make the selection random. Help is appreciated!
<?php
$images = get_field('project_documentation', 'option');
if( $images ): ?>
<?php
$i = 0;
foreach( $images as $image ):
$featured = get_field('featured_image', $image['id']);
if ($featured == '1' ) { ?>
<div class="gallery-image">
<img src="<?php echo $image['sizes']['large']; ?>" alt="<?php echo $image['alt']; ?>" />
</div>
<?php } $i++; endforeach; ?>
<?php endif; ?>

Answer 1

Assuming your code snippet worked (but lacks the random element), you could do something like the following.
<?php
$images = get_field('project_documentation', 'option');
if( $images ) {
$featured_images = array();
foreach( $images as $image ) {
$featured = get_field('featured_image', $image['id']);
if ($featured == '1' ) {
$featured_images[] = $image;
}
}
if ( !empty( $featured_images ) ) {
$rand = rand(0, count( $featured_images ));
$image = $featured_images[$rand];
?>
<div class="gallery-image">
<img src="<?php echo $image['sizes']['large']; ?>" alt="<?php echo $image['alt']; ?>" />
</div>
<?php
}
}