body{
    background-image: url('https://cdn.imgchest.com/files/3yrgceww564.gif');
    background-size: cover;
    padding:0;
    margin:0;
}

img {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 10%;
    margin-top: 10%;
    margin-bottom: 10%;
    opacity: .5;
    transition: .3s ease-in-out;
    
}   

img:hover{
    opacity: 1;
    content: url(https://cdn.imgchest.com/files/pyvdc2e6nby.gif);
}