Mod

altChecker.js

/* Modified version of Brian Bennett's bookmarklet for blurring
   images in a page lacking alt descriptions, added class for missing alts */

// code version
(function() {
    'use strict';

    function addCssRule(rule) {
        var head, style;
        head = document.querySelector('head');
        if (!head) { return; }
        style = document.createElement('style');
        style.type = 'text/css';
        style.innerHTML = rule;
        head.appendChild(style);
    }

    addCssRule("img[alt=''],img:not([alt] { filter: blur(10px) !important; outline: 10px solid !important; }");
})();

// This is version that can be used in bookmarklet

javascript: (function(){'use strict'; function addCssRule(rule){var head, style; head=document.querySelector('head'); if (!head){return;}style=document.createElement('style'); style.type='text/css'; style.innerHTML=rule; head.appendChild(style);}addCssRule("img[alt=''], img:not([alt]){filter: blur(10px) !important; outline: 10px solid !important;}");})();

For reference, https://blog.ohheybrian.com/2021/11/check-for-alt-tags-with-a-bookmarklet/