<img src="https://cdn.mos.cms.futurecdn.net/snbrHBRigvvzjxNGuUtcck.jpg" />

img{
  width: 200px;
  height: 200px;
  animation-name: fade-in-out;
  animation-duration: 3s;
  animation-iteration-count: infinite
}

@keyframes fade-in-out{
  0%{
    opacity: 1;
  }
   50%{
    opacity: 0;
  }
  100%{
    opacity: 1;
  }
}