I only included the construction of the image tag and not how the values are derived.
ACF image field would be set to return the ID, then with the ID you would use wp_get_attachment_image_src() using the ID and the $image_size you want as the maximum size. This gives you the url, width and height.
You would use other WP functions to some other method to get the alt and title values if you want to use them.
