<div class="image-slider">
<div><img src="http://csssecrets.io/images/adamcatlace-before.jpg" alt="Before" /></div>
<img src="http://csssecrets.io/images/adamcatlace.jpg" />
</div>

/**
 * Interactive image comparison - with CSS resize
 */

.image-slider {
	position:relative;
	display: inline-block;
}

.image-slider > div {
	position: absolute;
	top: 0; bottom: 0; left: 0;
	width: 50%;
	max-width: 100%;
	overflow: hidden;
	resize: horizontal;
}

.image-slider > div:before {
	content: '';
	position: absolute;
	right: 0; bottom: 0;
	width: 12px; height: 12px;
	padding: 5px;
	background: linear-gradient(-45deg, white 50%, transparent 0);
	background-clip: content-box;
	cursor: ew-resize;
	-webkit-filter: drop-shadow(0 0 2px black);
	filter: drop-shadow(0 0 2px black);
}

.image-slider img {
	display: block;
	user-select: none;
}