Wells
Wells provide a box to wrap images that should be presented on a background, most likely because they have transparency.
  Hello World
  <!-- Note: p-2 and m-2 are spacer helpers and not relevant to the example -->
<div class="well p-2 m-2">
  Hello World
</div>
They also come in multiple ratios and ensure that a contained image is resized to fill the space appropriatly.
Ratio 1:1
    Ratio 4:3
    Ratio 16:9
    <div class="layout">
  <div class="sm:col-2 lg:col-2 p-2">
    <h3>Ratio 1:1</h3>
    <div class="well well-1/1">
      <img src="/ember-logo.png" alt="Ember.js" />
    </div>
  </div>
  <div class="sm:col-2 lg:col-2 p-2">
    <h3>Ratio 4:3</h3>
    <div class="well well-4/3">
      <img src="/ember-logo.png" alt="Ember.js" />
    </div>
  </div>
  <div class="sm:col-2 lg:col-2 p-2">
    <h3>Ratio 16:9</h3>
    <div class="well well-16/9">
      <img src="/ember-logo.png" alt="Ember.js" />
    </div>
  </div>
</div>
Wells can be applied to anchors and work well with HTML <figure> elements.
<div class="layout">
  <div class="sm:col-2 lg:col-2 p-2">
    <figure>
      <div class="well well-16/9">
        <img src="/ember-logo.png" alt="Ember.js" />
      </div>
      <figcaption>
        A well thought out caption to add more information to the image above
      </figcaption>
    </figure>
  </div>
  <div class="sm:col-2 lg:col-2 p-2">
    <figure>
      <a href="#" class="well well-16/9">
        <img src="/ember-logo.png" alt="Ember.js" />
      </a>
      <figcaption>
        Using an anchor for the well works, too. You may want to add an additional link to the text
        and or make sure this becomes clear from the context.
      </figcaption>
    </figure>
  </div>
</div>