The code bellow uses mouse events to run a javascript function.
On line 15 the onmouseover and onmouseout events are used to call the function on line 6.
Line 7 targets the swap id and uses the argument passed to replace the image source.
<!doctype html> <html> <head> <script type="text/javascript"> function changeImage(img_src) { document.getElementById("swap").src = img_src; } </script> </head> <body> <h1>roll over</h1> <img id="swap" src="redButton.jpg" onmouseover='changeImage("blueButton.jpg")' onmouseout='changeImage("redButton.jpg")'> </body> </html>