将元素的尺寸设置为相等的响应图像尺寸

I'm building out flippable images on my site. I want the "back" of these images to have the same dimensions as the front. My problem is that I'm using the Bootstrap img-responsive class on my images so the "back" dimensions need to update dynamically to match the "front".I'm building out flippable images on my site. I