.frame {
    height: 160px; /* Can be anything */
    width: 160px; /* Can be anything */
    position: relative;
}
img {
    max-height: 100%;
    max-width: 100%;
    width: auto;
    height: auto;
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    margin: auto;
}