.about {
  .col-md-4 > div {
    position: relative;
    overflow: hidden;
    padding-bottom: 100%;

    img {
      position:absolute;
      width: 100%;
    }
  }
}

.about {
  .col-md-4 > div {
    position: relative;
    overflow: hidden;
    padding-bottom: 100%;

    img {
      position:absolute;
      min-width: 100%;
      min-height: 100%;
    }
  }
}

Make sure images are in a square dimension
Make sure images are in a square dimension
