No img-responsive in Bootstrap 4

It seems you need to use a new class img-fluid instead of img-responsive if you are using Bootstrap 4 alpha 2. Have a look at : http://v4-alpha.getbootstrap.com/content/images/

From the Bootstrap 4 documentation:

Images in Bootstrap are made responsive with .img-fluid. max-width: 100%; and height: auto; are applied to the image so that it scales with the parent element.

Bootstrap 3: .img-responsive

Bootstrap 4: .img-fluid

As in Bootstrap 4 Images:

Images in Bootstrap 4 are made responsive with .img-fluid. max-width: 100%; and height: auto; are applied to the image so that it scales with the parent element.

<img class="img-fluid" src="" alt=""> //This will make your image responsive