/**

* Convert an image

* to a base64 string

* @param {String} url

* @param {Function} callback

* @param {String} [outputFormat=image/png]

*/

function convertImgToBase64(url, callback, outputFormat){

var canvas = document.createElement("CANVAS"),

ctx = canvas.getContext("2d"),

img = new Image;

img.crossOrigin = "Anonymous";

img.onload = function(){

var dataURL;

canvas.height = img.height;

canvas.width = img.width;

ctx.drawImage(img, 0, 0);

dataURL = canvas.toDataURL(outputFormat);

callback.call(this, dataURL);

canvas = null;

};

img.src = url;

}

這個方法試試吧！！！！