<img src="https://hacks.mozilla.org/files/2017/06/omega.jpg" alt="Omega nebula" height="300">

img {
  -webkit-clip-path: polygon(50% 0%, 100% 25%, 100% 75%, 50% 100%, 0% 75%, 0% 25%);
  clip-path: polygon(50% 0%, 100% 25%, 100% 75%, 50% 100%, 0% 75%, 0% 25%);
  animation: 5s poly infinite alternate ease-in-out;
  margin: 1em auto;
  display: block;
}

@keyframes poly {
  from {
      -webkit-clip-path: polygon(50% 0%, 100% 25%, 100% 75%, 50% 100%, 0% 75%, 0% 25%);
      clip-path: polygon(50% 0%, 100% 25%, 100% 75%, 50% 100%, 0% 75%, 0% 25%);
  }
  
  to {
    -webkit-clip-path: polygon(44% 26%, 58% 38%, 58% 38%, 44% 81%, 44% 81%, 25% 49%);
    clip-path: polygon(44% 26%, 58% 38%, 58% 38%, 44% 81%, 44% 81%, 25% 49%);
  }
}