how to image responsive in bootstrap code example

Example 1: how to make image responsive bootstrap 4

<img src="..." class="img-fluid" alt="Responsive image">

Example 2: bootstrap Image thumbnails

In addition to our border-radius utilities, you can use 
.img-thumbnail to give an image a rounded 1px border appearance.

<img src="..." alt="..." class="img-thumbnail">

Example 3: img-fluid bootstrap

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

Example 4: img class bootstrap

<!-- Circuler Image -->
 <img src="cinqueterre.jpg" class="img-circle" alt="Cinque Terre"> 
 
<!-- Image With some border-raduis property  -->
 <img src="cinqueterre.jpg" class="img-rounded" alt="Cinque Terre"> 
 
<!-- Image like thumbnail  -->
 <img src="cinqueterre.jpg" class="img-thumbnail" alt="Cinque Terre">