Fitting a user-uploaded image of unknown aspect ratio into a fixed box has always meant a wrapper with overflow: hidden, the image absolutely positioned, and a centring translate. object-fit does it on the image itself.
.thumb {
width: 320px;
height: 180px;
object-fit: cover;
object-position: center;
}cover fills and crops, contain letterboxes — the same semantics as background-size, which is what people used to fake this with a div and lose the img semantics in the process. Firefox has had it since March and Chrome for a while; Safari and IE have not, so a wrapper fallback is still needed for anything customer-facing.