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）：

/***********************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  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： 

//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();