JSFiddle - React, Tailwind, and code Playground

HTML

<a href="http://google.com" class="darken">
    <img src="http://www.prelovac.com/vladimir/wp-content/uploads/2008/03/example.jpg" width="200">
</a>

CSS

a.darken {
    display: inline-block;
    background: black;
    padding: 0;
}

a.darken img {
    display: block;
}

JavaScript

$('.darken').hover(function() {
    $(this).find('img').fadeTo(500, 0.5);
}, function() {
    $(this).find('img').fadeTo(500, 1);
});