prowoke,
<a href="" onclick="this.src=this.src+'?'+Math.round(Math.ran dom())"><img src="/img/refresh_capcha.png" /></a>
Рабочий вариант
<img onclick="this.src=this.src+'?'+Math.round(Math.random())" src="/img/refresh_capcha.png" />
<!DOCTYPE html>
<html>
<head>
<title></title>
<script type="text/javascript">
var focus = function() {if (this.value == this.defaultValue) { this.value = ''; }};
var blur = function() {if (this.value == '') { this.value = this.defaultValue; }};
window.onload = function() {
document.myform.question.onfocus = focus;
document.myform.question.onblur = blur;}
</script>
</head>
<body>
<form name="myform" action="" method="post" id="myform">
<textarea cols="30" rows="5" name="question">
Введите свой вопрос
</textarea>
</form>
</body>
</html>