<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<script type='text/javascript' src="jquery-1.12.0.min.js"></script>
<script type='text/javascript' src="sc3.js"></script>
</head>
<body>
<p>Начало документа...</p>
<div>
<span onclick="ins(sp_icon)"><img id="sp_icon" src="arrow_right.gif">Текст</span>
</div>
<p>...Конец документа</p>
</body>
</html>
код js
function ins(id) {
var el = document.getElementById(id);
if (el.src === 'arrow_right.gif') el.src = 'arrow_down.gif'
else el.src = 'arrow_right.gif';
}