<div class="container">
                <label>请选择一个图像文件：</label>

                <input type="file" accept="image/gif,image/png,image/jpeg,image/jpg" id="file_input" multiple/>
                <button id="submit">提交</button>
            </div>
            <ul>
                <li>
                    <div class="pic_cover">
                        <img src="http://www.wangzhibo.top/wp-content/uploads/2018/06/%E5%BE%AE%E4%BF%A1%E5%9B%BE%E7%89%87_20180426142248-1-300x300.jpg" alt="证书封皮">
                        <span class="close"></span>
                    </div>
                </li>
            </ul>

<script src="http://libs.baidu.com/jquery/2.0.0/jquery.min.js"></script>
<script type="text/javascript">
 
 
window.onload = function(){
    var input = document.getElementById("file_input");
    var result,fd,dataArr = [];
    if(typeof FileReader==='undefined'){
        alert("抱歉，你的浏览器不支持 FileReader");
        input.setAttribute('disabled','disabled');
    }else{
        input.addEventListener('change',readFile,false);
    }
 
 
    function readFile(){
        fd = new FormData();
        var iLen = this.files.length;
        for(var i=0;i<iLen;i++){
            if (!input['value'].match(/.jpg|.gif|.png|.jpeg|.bmp/i)){　　//判断上传文件格式
                return alert("上传的图片格式不正确，请重新选择");
            }
            var reader = new FileReader();
            fd.append(i,this.files[i]);
            reader.readAsDataURL(this.files[i]);  //转成base64
            reader.fileName = this.files[i].name;
 
            reader.onload = function(e){
                var imgMsg = {
                    name : this.fileName,//获取文件名
                    base64 : this.result   //reader.readAsDataURL方法执行完后，base64数据储存在reader.result里
                }
                dataArr.push(imgMsg);
                result = '<div class="delete">delete</div><div class="result"><img class="subPic" src="'+this.result+'" alt="'+this.fileName+'"/></div>';
                var div = document.createElement('div');
                div.innerHTML = result;
                div['className'] = 'float';
                document.getElementsByTagName('body')[0].appendChild(div);  　　//插入dom树
                var img = div.getElementsByTagName('img')[0];
                img.onload = function(){
                    var nowHeight = ReSizePic(this); //设置图片大小
                    this.parentNode.style.display = 'block';
                    var oParent = this.parentNode;
                    if(nowHeight){
                        oParent.style.paddingTop = (oParent.offsetHeight - nowHeight)/2 + 'px';
                    }
                }
                div.onclick = function(){
                    $(this).remove();                  // 在页面中删除该图片元素
                }
            }
        }
    }
 
 
    /*function send(){
        var submitArr = [];
        $('.subPic').each(function () {
                submitArr.push({
                    name: $(this).attr('alt'),
                    base64: $(this).attr('src')
                });
            }
        );
        $.ajax({
            url : 'http://123.206.89.242:9999',
            type : 'post',
            data : JSON.stringify(submitArr),
            dataType: 'json',
            //processData: false,   用FormData传fd时需有这两项
            //contentType: false,
            success : function(data){
                console.log('返回的数据：'+JSON.stringify(data))
          　}
        })
    }*/
 
 
 
 
    /*oSelect.onclick=function(){
        oInput.value = "";   // 先将oInput值清空，否则选择图片与上次相同时change事件不会触发
        //清空已选图片
        $('.float').remove();
        oInput.click();
    }
 
 
    oAdd.onclick=function(){
        oInput.value = "";   // 先将oInput值清空，否则选择图片与上次相同时change事件不会触发
        oInput.click();
    }
 
 
    oSubmit.onclick=function(){
        if(!dataArr.length){
            return alert('请先选择文件');
        }
        send();
    }*/
}
/*
 用ajax发送fd参数时要告诉jQuery不要去处理发送的数据，
 不要去设置Content-Type请求头才可以发送成功，否则会报“Illegal invocation”的错误，
 也就是非法调用，所以要加上“processData: false,contentType: false,”
 * */
 
 
function ReSizePic(ThisPic) {
    var RePicWidth = 200; //这里修改为您想显示的宽度值
 
    var TrueWidth = ThisPic.width; //图片实际宽度
    var TrueHeight = ThisPic.height; //图片实际高度
 
    if(TrueWidth>TrueHeight){
        //宽大于高
        var reWidth = RePicWidth;
        ThisPic.width = reWidth;
        //垂直居中
        var nowHeight = TrueHeight * (reWidth/TrueWidth);
        return nowHeight;  //将图片修改后的高度返回，供垂直居中用
    }else{
        //宽小于高
        var reHeight = RePicWidth;
        ThisPic.height = reHeight;
    }
}
 
 

.float{
        float:left;
        width : 200px;
        height: 200px;
        overflow: hidden;
        border: 1px solid #CCCCCC;
        border-radius: 10px;
        padding: 5px;
        margin: 5px;
    }
    img{
        position: relative;
    }
    .result{
        width: 200px;
        height: 200px;
        text-align: center;
        box-sizing: border-box;
    }
 
 
    .delete{
        width: 200px;
        height:200px;
        position: absolute;
        text-align: center;
        line-height: 200px;
        z-index: 10;
        font-size: 30px;
        background-color: rgba(255,255,255,0.8);
        color: #777;
        opacity: 0;
        transition-duration: 0.7s;
        -webkit-transition-duration: 0.7s;
    }
 
 
    .delete:hover{
        cursor: pointer;
        opacity: 1;
    }