CSS how do you stretch to fit and maintain the aspect ratio?

I have the following css:

.mod.left {
background-image: url("http://www.myimage.jpg");
display: block;
height: 160px;
overflow: hidden;
width: 175px;
}

That corresponds to this HTML:

<div class="mod left"></div>

It results in this mess:

enter image description here

if I use the css3 background-size: 175px 160px; The aspect ratio is really messed up resulting in a mess like this:

enter image description here

Is there a way to stretch an image to fit a div? But in a way in which the aspect ratio is maintained? I want an auto crop.

html image css aspect-ratio

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