<div class="img-wrap">
  <img src="https://img-9gag-fun.9cache.com/photo/axzMvoW_460s.jpg" alt="">
</div>

.img-wrap {
  display: inline-flex;
  padding: 5px;
  border: 1px solid #000;
}

.img-wrap img {
  opacity: 0;
  transition: opacity .8s;
}

.img-wrap:hover img {
  opacity: 1;
}