I would recommend that you begin by having a look at a question asked more recently here. The best option would be to create a custom plugin so that the WP core doesn’t get affected. Editing core files is never a good idea, plus you would lose any changes when updating WP.
You can add inputs and fields to attachments by hooking into attachment_fields_to_edit. This will add fields to both the modal as well as the attachment editor. The catch I found is that WordPress (if anyone has experienced differently PLMK) doesn’t save the extra fields data so you have to hook into a couple other items. … Read more
This will add a field in the attachment edit screen for applying a class to the img tag. function IMGattachment_fields($form_fields, $post) { $form_fields[“imageClass”][“label”] = __(“Image Class”); $form_fields[“imageClass”][“value”] = get_post_meta($post->ID, “_imageClass”, true); return $form_fields; } add_filter(“attachment_fields_to_edit”, “IMGattachment_fields”, null, 2); function my_image_attachment_fields_save($post, $attachment) { if ( isset($attachment[‘imageClass’]) ) update_post_meta($post[‘ID’], ‘_imageClass’, $attachment[‘imageClass’]); return $post; } add_filter(“attachment_fields_to_save”, “my_image_attachment_fields_save”, null, … Read more