<div class="container">
  <div class="row">
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
    <div class="col-6 col-sm-4 col-md-3 col-lg-3">
      <img src="https://images.unsplash.com/photo-1528313316397-ddee14ed98f0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2250&q=80" alt="Cute Animal" />
    </div>
  </div>
</div>

img {
  max-width: 100%;
  padding-bottom: 1rem;
}