Bootstrap 4

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.2/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.2/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootswatch/3.3.7/flatly/bootstrap.min.css">
<div class="container">
    <div class="row imagetiles">
        <div class="col-lg-3 col-md-3 col-sm-3 col-xs-6">
            <img src=https://i.imgur.com/nXSiWbw.jpg class="img-responsive">
        </div>
        <div class="col-lg-3 col-md-3 col-sm-3 col-xs-6">
            <img src=https://i.imgur.com/0dXOdvZ.jpg class="img-responsive">
        </div>
        <div class="col-lg-3 col-md-3 col-sm-3 col-xs-6">
            <img src=https://i.imgur.com/nXSiWbw.jpg class="img-responsive">
        </div>
        <div class="col-lg-3 col-md-3 col-sm-3 col-xs-6">
            <img src=https://i.imgur.com/0dXOdvZ.jpg class="img-responsive">
        </div>
    </div>
</div>

CSS

div.imagetiles div.col-lg-3.col-md-3.col-sm-3.col-xs-6{
  padding: 0px;
}

.imagetiles {
 align-items: center;
 display: flex;
}