How to center image cropping (<img>) in a fluid-width container
How do I get an image so that it remains centered when the liquid container (based on percentages) is too small to show the whole image?

How to center an image inside a container
This means that it should show the middle of the image instead of the sides when the container is too small.
When he works
You may have a container that contains some content, such as two <div> , which are 50% wide each, sitting next to each other. In this example, we can illustrate only one child of the container: 
We will call the outer rectangle .container , the inner rectangle .content and the image img . This layout is beautiful, as long as .content always wider than img .
When he breaks
Since we are dealing with interest and are probably working with a responsive design, this may not always be the case. If .content always thinner than img , trimming will occur:

Problem
If the most interesting part of img is in the center, we need to make the browser crop both edges evenly - leaving most of it visible, regardless of the width of the .content .

Decision
Fortunately, a solution is possible. Moreover, additional markup is not required.
.content { width: 90%; /* or whatever is required */ text-align: center; /* ensures the image is always in the h-middle */ overflow: hidden; /* hide the cropped portion */ } img { position: relative; /* allows repositioning */ left: 100%; /* move the whole width of the image to the right */ margin-left: -200%; /* magic! */ } For new browsers you can translate it
figure{ width: 100%; text-align: center; overflow: hidden; } img{ position: relative; left: 50%; transform: translate(-50%,0) } To support IE8, you can still use the technique provided by @BryceHanscomb above.
.no-csstransforms figure img { left: 100%; /* move the whole width of the image to the right */ margin-left: -200%; /* magic! */ } If you expect the image to be displayed to be much larger than the display container by setting to the left: 100%; and margin-left: -200%; (from Bryza’s answer) may not be enough to get the center of the image. Just put a higher percentage for both. Make sure the other is half the other, though.
left: 500%; margin-left: -1000%;