Put any of your two images in folder images/
<!doctype>
<html>
<head>
<script>
function changeImage(img){
var imgfile = img.src.split('/').pop();
if(imgfile == "happy.png")
{
img.src ="images/sad.png";
}
else{
img.src = "images/happy.png";
}
}
</script>
</head>
<body>
<img src='images/happy.png' onclick='changeImage(this)'>
</body>
Online Demo
<!doctype>
<html>
<head>
<script>
function changeImage(img){
var imgfile = img.src.split('/').pop();
if(imgfile == "happy.png")
{
img.src ="images/sad.png";
}
else{
img.src = "images/happy.png";
}
}
</script>
</head>
<body>
<img src='images/happy.png' onclick='changeImage(this)'>
</body>
Online Demo
