页面要做一个截图的功能，本地生成了一张图片，然后转成canvas，再从canvas变成png，但是canvas.toDataUrl()一直报错：

Uncaught DOMException: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.

代码如下：

var url = DOMURL.createObjectURL(svg);
        var canvas = document.createElement('canvas');
        var ctx = canvas.getContext('2d');
        canvas.width = window.innerWidth;
        canvas.height = window.innerHeight*1.25;
        cacheImg(url,function(){
            ctx.drawImage(this , 0 , 0);
            var image = canvas.toDataURL("image/png").replace("image/png", 'image/octet-stream');
            DOMURL.revokeObjectURL(url);
        });
        
        function cacheImg(url , callback){
            var img = new Image()
            img.setAttribute('crossOrigin', 'Anonymous');
            img.src = url;
            img.onload = function() {
                callback.call(img)
            }
        }