ImageReplacer.user.js

// ==UserScript==
// @name         Image Replacer
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Replaces all images with base64
// @author       You
// @match        https://*/*
// @grant        none
// @require      https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js
// ==/UserScript==

(function() {
    'use strict';
    var images = $('img');
    var base = 'https://zv3.herokuapp.com/b64/?url=';
    for (var key in images) {
        let current = images[key];
        let src = current.src;
        //console.log(src);]
        if (src == undefined) continue;
        if (src.startsWith('data:image/')) return;
        $.get(base + src,(data) => {
            //$(current).attr('src',data);
            current.src = data;
            //current.attr('onerror', "this.src=http://kindersay.com/files/images/hamburger.png");
            //console.log(current.src);
        });
    }
})();