On the following page you make recommendation that I feel is not correct. I know in my case it cost me a couple of hours.
http://www.w3schools.com/html/html_images.asp
Please note the following statements: " We suggest you use the style attribute. "
If you are using Bootstrap this will interfere with the responsive nature of the image as the size of the screen changes. I suspect this would apply to other responsive frame works.
You should either delete the recommendation or note the effect on responsive frame works.