How to make an image resize to the screens height with CSS?

Question

Unlike many people who want an image to fill out the whole screen, I only care about the image height. How can I use CSS (preferably not JavasScript) to make an image with any size, fill up to 100% of the maximum possible browser window height while keeping aspect ratio of the image, the re-sized width of the image in respect to the browser does not matter.

I'm working with this html:

<div class="images">
  <img/>
</div>

Thank you so much!

Answer 1

This might be overkill:

.img {
    position: absolute;
    height: 100%;
    top: 0;
    bottom: 0;
}