If setting a fixed width on the image is not an option, here's an alternative solution.
Having a parent div with display: table & table-layout: fixed. Then setting the image to display: table-cell and max-width to 100%. That way the image will fit to the width of its parent.
Example:
<style>
.wrapper { float: left; clear: left; display: table; table-layout: fixed; }
img.img-responsive { display: table-cell; max-width: 100%; }
</style>
<div class="wrapper col-md-3">
<img class="img-responsive" src="https://www.google.co.uk/images/srpr/logo11w.png"/>
</div>
Fiddle: http://jsfiddle.net/5y62c4af/