Demo

index.html
style.css

<!DOCTYPE html>
<html>
	<head>
		<meta name="viewport" content="width=device-width, initial-scale=1">
		<link href="/assets/styles/reset.css" rel="stylesheet">
		<link href="style.css" rel="stylesheet">
	</head>
	<body>
		<section>
			<picture>
				<source media="(max-width: 428px)" srcset="tim.jpg">
				<source media="(max-width: 640px)" srcset="tim--md.jpg">
				<img alt="Tim Berners-Lee at a computer." src="tim--lg.jpg">
			</picture>
		</section>
	</body>
</html>

body, section { padding: 20px; }

section { background-color: gold; }