Images
Images can be responsive to fit the parent's width, and also can be customised to be round shaped
Responsive Image
You can add class img-responsive to make your image fit the width of container. It's height will get adjusted by keeping the aspect ratio same. If you want to change the aspect ratio, you will have to crop the image.
Round Image
You can add class img-round to make your image round shaped. You should give equal height and width to container of image.