<!doctype html>
<style>
img {
object-fit: scale-down;
object-position: 0 0;
}
div {
width: 1000px;
height: 1000px;
background-color: blue;
}
</style>
<div>
<img src="resources/blue-100-px-square.png"
srcset="resources/blue-100-px-square.png 100w,
resources/green-400-px-square.png 400w">
</img>
</div>