圖片img:滑鼠滑過變換圖片

(1).圖片標籤<img id="img01" onmouseup="show04()" onmousedown="show03()" onmouseout="show02()" onmouseover="show01()" src="icon80_80/image01.jpg" width="74" height="74" />
(2).滑鼠滑過事件:onmouseover
(3).滑鼠離開事件:onmouseout
(4).滑鼠按下事件:onmousedown
(4).滑鼠放開事件:onmouseup