.img-wrapper{
    display: block;
    position: relative;
    width: 300px;
}
.img-wrapper img{
    max-width: 100%;
    display: block;
}
.img-wrapper :nth-child(2){
    display: none;
}
.img-wrapper:hover :nth-child(2){
    display: block;
}
.img-wrapper:hover :first-child{
    display: none;
}