Making Media Library “Alternative Text” Field Required

I’ve managed to make it work of sorts…

The requirement is not checked in the Media Library upload /wp-admin/media-new.php, but instead in the Media Upload thickbox iframe /wp-admin/media-upload.php.

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The following is the code that works in the thickbox and displays an alert box making mandatory filling the Alt text field.
_{IMO, it won’t be easy, but it can be adapted to work in the Upload New Media page (/wp-admin/media-new.php)…}

add_action('admin_head-media-upload-popup','wpse_55240_required_alt_text');
function wpse_55240_required_alt_text()
{
    ?>
    <script language="javascript" type="text/javascript">
        jQuery(document).ready(function($) {
            $(".submit .savesend input").live("click", validateAltText);

            function validateAltText() {
                var value = $(this).parent().parent().parent().find(".image_alt input").val();

                if (value) 
                    return true;

                alert("Please fill the Alt text");
                return false;
            }

            $('.image_alt th label').each(function(i,e) {
                $('<span class="alignright"><abbr title="required" class="required">*</abbr></span>').prependTo(this);
            });

        });
    </script>
<?php
}