var pics = {
"one": "https://image.freepik.com/free-photo/cute-cat-picture_1122-449.jpg",
"two": "https://media.wired.com/photos/598e35fb99d76447c4eb1f28/master/pass/phonepicutres-TA.jpg",
"three": "https://c1.staticflickr.com/2/1520/24330829813_944c817720_b.jpg"
}
function check_value(event){
document.getElementById("imagetest").src = pics[event.target.value] ;
}