JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css">
<div class="bs-example">
    <div class="container">
        <div class="row">
            <div class="col-xs-3">
                <a href="#" class="thumbnail">
                    <img src="http://exmoorpet.com/wp-content/uploads/2012/08/cat.png">
                </a>
            </div>
            <div class="col-xs-3">
                <a href="#" class="thumbnail">
                    <img src="http://www.nose2tail.co.uk/cat-matlock-derbyshire.jpg" alt="125x125">
                </a>
            </div>
            <div class="col-xs-3">
                <a href="#" class="thumbnail">
                    <img src="http://www.us.onsior.com/images/3_1/cat-3_1-01.png">
                </a>
            </div>
            <div class="col-xs-3">
                <a href="#" class="thumbnail">
                    <img src="https://www.petfinder.com/wp-content/uploads/2012/11/155293403-cat-adoption-checklist-632x475-e1354290788940.jpg" >
                </a>
            </div>
        </div>
    </div>
</div>

CSS

.thumbnail {
    height: 100px;
}

.thumbnail img {
    max-height: 100%;
    max-width: 100%;
    border: 1px solid red;
}