Woocommerce Responsive Product Images with CSS

Looking at your page, I can see you have a full image http://cloud9slo.com/wp-content/uploads/2014/10/home-slider-cloud-9-slo.jpg  at 1920 × 577.

The rendered code around the image has the following

element.style {
width: 100%;
height: 100%;
opacity: 1;
visibility: inherit;
background-image: url(http://cloud9slo.com/wp-content/uploads/2014/10/home-slider-cloud-9-slo.jpg);
background-color: rgba(0, 0, 0, 0);
background-size: cover;
background-position: 50% 0%;
background-repeat: no-repeat;
}

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Since you are using "cover", the image could be stretched at something other than the original ratio of width and hight.  Your images should be at 100% for the best image quality and for sure the same ratio.

The ratio of the image on the site is 2.744 where the original image is 3.23.  To get this ratio, I am dividing the width and height.  Because the the rendered ratio is different than the original, it is not going to be as crisp.  

If you are using the woo plug in, it might be easier to just keep it as is.  The other option is to crop your image at the same ratio the plug in uses.  The last option is to recode that area yourself.  

Cropping the images may be easier.  Take note if you can use different images for different breaks in media queries as your image ratio may change.

Thanks for the reply Scott. The slider image http://cloud9slo.com/wp-content/uploads/2014/10/home-slider-cloud-9-slo.jpg is adjusting fine to various browser widths and maintains quality.

 It's the Single product images i'm having trouble keeping crisp while adjusting the browser window. > http://s8.postimg.org/jqbm5net1/Screen_Shot_2014_12_03_at_2_56_48_PM.png