<img class="opacity"src="https://citaty.info/files/styles/poster/public/characters/144853.jpg?itok=hdpicg0G" alt="">
.opacity {
opacity:0.3;
cursor:pointer;
}
.active {
opacity: 1;
}
let opacity = document.querySelector('.opacity');
opacity.addEventListener('click', function(){
opacity.classList.toggle('active');
})
This Pen doesn't use any external CSS resources.