Fix aspect ratio of images by zooming. This will "crop" your image.

gallery.html

<div class="img" style="background-image:url('http://i.imgur.com/tI5jq2c.jpg');"></div>
<div class="img" style="background-image:url('http://i.imgur.com/37w80TG.jpg');"></div>
<div class="img" style="background-image:url('http://i.imgur.com/B1MCOtx.jpg');"></div>

<style>
.img {
    position: relative;
    float: left;
    width:  100px;
    height: 100px;
    background-position: 50% 50%;
    background-repeat:   no-repeat;
    background-size:     cover;
}
</style>