//计算图片md5

        function img_MD5(img_path,callback) {

            plus.io.resolveLocalFileSystemURL(img_path, function(entry) {

                var fileReader = new plus.io.FileReader();

                fileReader.readAsDataURL(entry);

                fileReader.onloadend = function(evt) {

                    var format="image/jpeg";

                    //抽取DataURL中的数据部分，从Base64格式转换为二进制格式

                    var bin = atob(evt.target.result.split(',')[1]);

                    //创建空的Uint8Array

                    var buffer = new Uint8Array(bin.length);

                    //将图像数据逐字节放入Uint8Array中

                    for (var i = 0; i < bin.length; i++) {

                        buffer[i] = bin.charCodeAt(i);

                    };

                    //利用Uint8Array创建Blob对象

                    blob = new Blob([buffer.buffer], {type : format});

                    var fileReader1 = new FileReader();

                    fileReader1.readAsBinaryString(blob);

                    fileReader1.onload = function(evt) {

                        if (evt.target.readyState == FileReader.DONE) {

                            var imgblob = evt.target.result;

                            var sparkMD5 = new SparkMD5();

                            sparkMD5.appendBinary(imgblob);

                            var MD5 = sparkMD5.end();

                            console.log("MD5:" + MD5);

                            callback(MD5)

                        }

                    };

                }

            }, function(e) {

                console.log("Resolve file URL failed: " + e.message);

            });

        }

//使用方法

var url=document.getElementById("ID").src;

img_MD5(url,function (md5){

                    console.log(md5)

                })