Get Meta from Custom Field of Image URL

I can already tell that you’re using ACF – if you don’t want to change the return settings for the field, you can bypass ACF and just pull the image ID directly from post meta:

$image_url  = get_field( 'my_field_name' );
$image_id   = get_post_meta( $post->ID, 'my_field_name', true );
$image_meta = wp_get_attachment_metadata( $image_id );