Thumbnail
<img alt="" class="img-fluid img-thumbnail" src="/sites/default/files/theme/image-dummy-square.jpg" />
Rounded
<img alt="" class="img-fluid rounded" src="/sites/default/files/theme/image-dummy-square.jpg" />
Circle
<img alt="" class="img-fluid rounded-circle" src="/sites/default/files/theme/image-dummy-square.jpg" />