JSFiddle - React, Tailwind, and code Playground

HTML

<img src="/pix/31/image.jpg" class="fos" alt="" />
<img src="/pix/image.gif" class="fos" alt="" />
<img src="/pix/image31.jpg" class="fos" alt="" />
<img src="/pix/moka/31.valami.jpg" class="fos" alt="" />

CSS

img { width: 100px; height: 100px; }
.fos { border: 1px solid red; }

JavaScript

$('img').removeClass(function () {
    if (this.src.replace(/^.*\//, '').indexOf('31') > -1) {
         return 'fos';
    }
    return false;
});