JSFiddle - React, Tailwind, and code Playground

HTML

<img src="https://media.starwars.ea.com/content/starwars-ea-com/it_IT/starwars/galaxy-of-heroes/_jcr_content/ogimage.img.jpg" width="320" height="240">

CSS

img:hover {
  -webkit-filter: grayscale(0%);
  -webkit-transition: .5s ease-in-out;
  -moz-filter: grayscale(0%);
  -moz-transition: .5s ease-in-out;
  -o-filter: grayscale(0%);
  -o-transition: .5s ease-in-out;
  filter: grayscale(0%);
} 

img {
  -webkit-filter: grayscale(100%);
  -webkit-transition: .5s ease-in-out;
  -moz-filter: grayscale(100%); 
  -moz-transition: .5s ease-in-out;
  -o-filter: grayscale(100%); 
  -o-transition: .5s ease-in-out;
  filter: grayscale(100%);
}