<script>
function fsrc(n){
document.getElementById("images").src=n;
}
</script>
<select onclick="if(this.value)(fsrc(this.value))">
<option value="1.jpg">option 1</option>
<option value="2.jpg">option 2</option>
<option value="3.jpg">option 3</option>
</select>
<img id="images" src="">