I do a catalog using Bootstrap 3. When displayed on tablets, the product images look ugly because of their small size (500x500) and a width of 767 pixels in the browser. I w
If you're using Bootstrap v3.0.1 or greater, you should use this solution instead. It doesn't override Bootstrap's styles with custom CSS, but instead uses a Bootstrap feature.
My original answer is shown below for posterity
This is a pleasantly easy fix. Because .img-responsive from Bootstrap already sets display: block, you can use margin: 0 auto to center the image:
.product .img-responsive {
margin: 0 auto;
}