Advanced Custom Fields (ACF) Plugin – Random Image in Sidebar

You aren’t getting an image because you are calling the image field outside the query loop.

<?php $args = array( 
    'post_type' => 'slide', 
    'posts_per_page' => 1, 
    'orderby' => rand
);

// url = $image[0];
// width = $image[1];
// height = $image[2];

$loop = new WP_Query( $args );
while ( $loop->have_posts() ) : $loop->the_post();
    $attachment_id = get_field('slide_photo');
    $size = "medium"; // (thumbnail, medium, large, full or custom size)
    $image = wp_get_attachment_image_src( $attachment_id, $size );

    echo '<img src="';
    echo $image[0];
    echo '" />';
    the_title();
    the_field('slide_credit');

endwhile; ?>