先看效果图：

要求：当输入框获得焦点时，自动显示验证图片。
代码如下（学习而已，仅供参考）：
复制代码 代码如下:
/***********************下是验证码对象*****************/
var Validation = {};
Validation.init = function(eleName,imageSrc){
this.image = imageSrc;
$('#'+eleName).focusin(function(){
Validation.show(eleName);
});
}
Validation.image = '';
Validation.display=false;
Validation.width = '100px';
Validation.height = '30px';
Validation.div = null;
Validation.show = function(eleName){
if(this.display==false){
//首次显示
if(this.div==null){
$('#'+eleName).after('<div style="display:none;" id="div_validation_'+eleName+'" title="点击更换"></div>');
this.div = $('#div_validation_'+eleName);
this.div.css('position','absolute');
this.div.css('cursor','pointer');
this.div.css('border','1px solid #CCC');
this.div.css('background-color','#FFF');
this.div.css('background-position','center');
this.div.css('background-repeat','no-repeat');
this.div.css('height',this.height);
this.div.css('width',this.width);
var objOffset = $('#'+eleName).offset();
objOffset.top+=$('#'+eleName).height()+6;
this.div.offset(objOffset);
this.div.css('background-image','url('+Validation.image+'&_t='+new Date()+')');
this.div.css('display','inline-block');
this.display = true;
//点击更换
this.div.click(function(){
Validation.div.css('background-image','url('+Validation.image+'&_t='+new Date()+')');
});
}
else{
this.div.css('background-image','url('+Validation.image+'&_t='+new Date()+')');
this.display = true;
this.div.css('display','inline-block');
}
}
}
Validation.hide =function(){
if(this.display==true){
this.display = false;
this.div.hide();
}
}

使用方式：
复制代码 代码如下:
//验证码对象初始化
Validation.init('validation','Ajax.ashx?handle=validation');
// 输入框ID 验证图片地址
//隐藏
Validation.hide();