function lighton()
{
document.getElementById('myimage').src="//www.w3school.com.cn/i/eg_bulbon.gif"
}
function lightoff()
{
document.getElementById('myimage').src="//www.w3school.com.cn/i/eg_bulboff.gif"
}
<img id="myimage" onmousedown="lighton()" onmouseup="lightoff()" src="//www.w3school.com.cn/i/eg_bulboff.gif" width="100" height="180">
<p>请点击灯泡，把它点亮！</p>