Accurate Polaroid reveal effect

reveal.css

/* See in action at https://codepen.io/juancroldan/pen/vYVLYBx */

.polaroid {
  background: #eeefea;
  box-shadow: 0 0 .5px 1px #5415;
  border-radius: 3px;
}
.polaroid img {
  width: 230px;
  height: 305px;
  margin: 42px 17px 83px;
	display: block;
  object-fit: cover;
  background: #e8e1d6;
  filter: contrast(0) sepia(1.6) contrast(.2) brightness(1.7) blur(.5px);
  transition: filter 12s 2s linear;
  border-radius: 2px;
	box-shadow: 0 0 200px rgba(0,0,0,0.9) inset;
}
.polaroid.squared img {
  width: 316px;
  height: 316px;
  margin: 22px 18px 90px;
}
.polaroid.reveal img {
  filter: contrast(0.8) sepia(0.3) contrast(1) brightness(1.2) blur(.5px);
}