If you're wondering how to add responsive images to certain parts of shop like product descriptions, cms pages contents etc check video guide that is attached below. Each time you will include picture to the shop in description fields, you will notice that these pictures aren't reponsive. When you will use mobile device to see how the pictures appear, you will see that these pictures are to big for mobile devices. They will be cutted etc. 

it's a case of styles that bootstrap uses, it will be necessary to add class="" param with "img-responsive" class. You can achieve it very easily with tools available in tinymce editor. Check vide below if it is still unknow thing for you.