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 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：

//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();

以上就是本文的全部内容，希望对大家的学习有所帮助。