Wordpress customize add media

Question

I am creating a checkbox in the Add Media popup screen to add HTML to the $html output when inserting an image.

This is working fine. However, once I have added an image with the checkbox selected. If I try and add it again, and deselect the checkbox, it won't register or save the change.

Thus always outputting the modified image instead of reverting back to WP default once unchecked.

Plus the check mark after I have selected it and inserted to page will stay pre-selected every time I select that image.

How do I make the unselect checkbox function as would be expected?

Much appreciate the help. Thanks

class media_uploader_cb{

    function __construct(){
        // attach our function to the correct hook
        add_filter('attachment_fields_to_edit',  array( $this, 'attachment_fields_to_edit' ), 10, 2);
        //save attachment field
        add_filter( 'attachment_fields_to_save', array( $this, 'attachment_fields_to_save' ), 10, 2);
        //add custom css class
        add_filter( 'media_send_to_editor',      array( $this, 'media_send_to_editor' ), 10, 2 );
    }

    /**
     * Adding our custom checkbox field to the $form_fields array
     * 
     * @param array $form_fields
     * @param object $post
     * @return array
     */
    function attachment_fields_to_edit($form_fields, $post) {
        $form_fields['add_class']['label'] = __("Add SEO Data");
        $form_fields['add_class']['input'] = 'html';
        $form_fields['add_class']['html'] = '<input type="checkbox" value="1" name="attachments['.$post->ID.'][add_class]" id="attachments['.$post->ID.'][add_class]" '.checked( 1, get_post_meta($post->ID, 'add_class', true), false ).'/>';
        return $form_fields;
    }


    /**
     * Saving our custom checkbox field
     * @param array $post
     * @param array $attachment
     * @return array
     */
    function attachment_fields_to_save($post, $attachment) {

        if( isset($attachment['add_class']) ){
            update_post_meta($post['ID'], 'add_class', $attachment['add_class']);
        }
        return $post;
    }

    /**
     * Adding our custom css class based on checkbox field 
     * 
     * @param string  $html
     * @param int $id
     * @return string
     */
    function media_send_to_editor( $html, $id ) {
        //only add class if the checkbox was checked
        if ( 1 == (int)get_post_meta($id, 'add_class', true) ){
            //change this to whatever you want
            $seo_data_to_add = 'custom="HTML Output Here""';

            // THIS SHOULD BE THE CHECKBOX
            get_post_meta($id, 'add_class', true);

            $attachment_title = get_the_title($id);
            $title = 'title="'.$attachment_title .' by '. get_option('ews_opt_branding') .'"';
            $html = str_replace('<img', '<img '.$title.' '.$seo_data_to_add.'', $html);
        }
        return $html;
    }


}

new media_uploader_cb();

Answer 1

Got some assistance from another forum. It spurred some brainstorming at the office and we came up with a solution. Not sure if this is the best way to resolve it but it is working as expected. I added this code:

delete_post_meta($id, 'add_class', true);

just above the:

return $html;

at the end of the last function and everything is behaving properly. If there is a better solution, please let me know.