bootstrap css image thumbnail code example
Example 1: image responsive bootstrap 4
<img class="img-fluid" src="" alt=""> //This will make your image responsive
Example 2: bootstrap Aligning images
Align images with the helper float classes or text alignment classes.
block-level images can be centered using the .mx-auto margin utility class.
<img src="..." class="rounded float-left" alt="...">
<img src="..." class="rounded float-right" alt="...">
<img src="..." class="rounded mx-auto d-block" alt="...">