A pure css solution

Requiring one extra wrapper (tested in FireFox, IE8, IE7):

Improved Answer

There was a problem with the original answer (below). If the image is larger than the container that outer is centered on with it’s auto margins, then it truncates the image on the left and creates excessive space on the right, as this fiddle shows.

We can resolve that by floating inner right and then centering from the right. This still truncates the img off the page to the left, but it does so by explicitly pushing it that way and then centers back off of that, the combination of which is what prevents the extra horizontal scroll on the right. Now we only get as much right scroll as we need in order to see the right part of the image.

Fiddle Example (Borders in fiddle are for demo only.)

Essential CSS

div.outer {
    width: 300px; /* some width amount needed */
    margin: 0 auto; 
    overflow: visible;
}
div.inner {
    position:relative;
    float: right; /* this was added and display removed */
    right: 50%;
}
div.inner img {
    position: relative; 
    right:-50%; /* this was changed from "left" in original */
}

If you desire no right scroll at all for wide images

Then using the above, also set whatever element wraps outer (like body or a third wrapper) to have overflow: hidden.

Original Idea (for History)

Fiddle Example (Borders in fiddle are for demo only.)

HTML

<div class="outer">
    <div class="inner">
        <img src="https://stackoverflow.com/yourimage.png">
    </div>
</div>

CSS

div.outer {
    width: 300px; /* some width amount needed */
    margin: 0 auto; 
    overflow: visible;
}
div.inner {
    display: inline-block; 
    position:relative; 
    right: -50%;
}
div.inner img {
    position: relative; 
    left:-50%; 
}