bootstrap 4 center image
/* used mx-auto d-block */
<img class="mx-auto d-block" src="https://www.w3schools.com/bootstrap4/paris.jpg" alt="https://www.w3schools.com/bootstrap4/paris.jpg"/>bootstrap class align center image
class="mx-auto d-block"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="...">Source: getbootstrap.com