how to add legend on images bootstrap code example

Example: bootstrap Figures

Anytime you need to display a piece of content—like an image with an optional
caption, consider using a <figure>.

Use the included .figure , .figure-img and .figure-caption classes to provide
some baseline styles for the HTML5 <figure> and <figcaption> elements.
Images in figures have no explicit size, so be sure to add 
the .img-fluid class to your <img> to make it responsive.

<figure class="figure">
  <img src="..." class="figure-img img-fluid rounded" alt="...">
  <figcaption class="figure-caption">A caption for the above image.</figcaption>
</figure>

<figure class="figure">
  <img src="..." class="figure-img img-fluid rounded" alt="...">
  <figcaption class="figure-caption text-right">A caption for the above image.</figcaption>
</figure>