html, body {
    width: 100%;
    height: 100%;
    display: flex;
}


div {
    margin: auto;
    position: relative;
    width: 300px;
    height: 180px;
    background: url(https://www.cdsy.xyz/images/kszt.png) no-repeat;
    background-size: cover;
    mask:
        linear-gradient(135deg, transparent 15px, #fff 0)
        top left,
        linear-gradient(-135deg, transparent 15px, #fff 0)
        top right,
        linear-gradient(-45deg, transparent 15px, #fff 0)
        bottom right,
        linear-gradient(45deg, transparent 15px, #fff 0)
        bottom left;
    mask-size: 50% 50%;
    mask-repeat: no-repeat;
}