<img src="https://picsum.photos/id/1069/250/250" >
<img src="https://picsum.photos/id/1011/250/250" >

img {
  --m:
    radial-gradient(circle farthest-side at right,#000 99%,#0000) 
      0 100%/46% 92% no-repeat,
    radial-gradient(circle farthest-side at left ,#000 99%,#0000) 
      100% 0/46% 92% no-repeat;
  -webkit-mask: var(--m);
          mask: var(--m);
  filter: grayscale(.5);
  transition: .3s linear;
  cursor: pointer;
}
img:hover {
  -webkit-mask-position: 7.5% 50%,92.5% 50%;
          mask-position: 7.5% 50%,92.5% 50%;
  filter: grayscale(0);
}

body {
  margin: 0;
  background: #ccc;
  display: grid;
  height: 100vh;
  grid-auto-flow :column;
  place-content: center;
  gap: 40px;
}