Is it possible to scale an image proportionally both on width and height based on a fixed container?

Question

Suppose we have an image that is 400x200 and another that is 200x400 and I want them to fit in a 200x200 box so the first should be scaled to 200x100 and the second to 100x200

We won't know the dimensions of the images in advance.

[edit] Plenty of good answers, thank you all!

Answer 1

One way is to use object-fit:

img {
  object-fit: contain;
  width: 200px;
  height: 200px;
}

JSFiddle Demo: https://jsfiddle.net/t75cxqt0/2/