canvas.toDataURL() SecurityError

Question

So I'm using google maps and I get the picture so it looks like this

<img id="staticMap"
        src="http://maps.googleapis.com/maps/api/staticmap?center=Brooklyn+Bridge,New+York,NY&zoom=13&size=600x300&maptype=roadmap
&markers=color:blue%7Clabel:S%7C40.702147,-74.015794&markers=color:green%7Clabel:G%7C40.711614,-74.012318
&markers=color:red%7Ccolor:red%7Clabel:C%7C40.718217,-73.998284&sensor=false">

I need to save it. I have found this:

function getBase64FromImageUrl(URL) {
    var img = new Image();
    img.src = URL;
    img.onload = function() {

        var canvas = document.createElement("canvas");
        canvas.width = this.width;
        canvas.height = this.height;

        var ctx = canvas.getContext("2d");
        ctx.drawImage(this, 0, 0);

        var dataURL = canvas.toDataURL("image/png");

        alert(dataURL.replace(/^data:image\/(png|jpg);base64,/, ""));

    };
}

But I get this problem:

Uncaught SecurityError: Failed to execute 'toDataURL' on 'HTMLCanvasElement': tainted canvases may not be exported.

I searched for fixes. I found a sample here How to use CORS but still I can't tie these 2 pieces of code together to make it work. Maybe I'm doing it the wrong way and there is a simpler way to do it? I'm trying to save this pic so that I can transfer the data to my server. So maybe someone did something like this and knows how to make .toDataURL() work as I need it?

Broider

Answer 1

Unless google serves this image with the correct Access-Control-Allow-Origin header, then you wont be able to use their image in canvas. This is due to not having CORS approval. You can read more about this here, but it essentially means:

Although you can use images without CORS approval in your canvas, doing so taints the canvas. Once a canvas has been tainted, you can no longer pull data back out of the canvas. For example, you can no longer use the canvas toBlob(), toDataURL(), or getImageData() methods; doing so will throw a security error.

This protects users from having private data exposed by using images to pull information from remote web sites without permission.

I suggest just passing the URL to your server-side language and using curl to download the image. Be careful to sanitise this though!

EDIT:

As this answer is still the accepted answer, you should check out @shadyshrif's answer, which is to use:

var img = new Image();
img.setAttribute('crossOrigin', 'anonymous');
img.src = url;

This will only work if you have the correct permissions, but will at least allow you to do what you want.

Ridge

I'd take the remote alternative suggestion from @Ridge further and propose making it the default behaviour. The server will almost certainly be able to receive the img.src then wget*/*cURL the image quicker than the client could encode a local-origin image and POST it to the server. Perhaps, only if client-side authentication is required (i.e. your server's attempt ends with a 403), you could fall-back to using canvas.toDataURL(img) in the hopes that it's being served from the same origin as the page. This default behaviour will also result in the original file (EXIF et al.) – Brophy

I have set my Google Cloud Storage bucket to "Access-Control-Allow-Origin: *" yet I still get this security error when trying to use the toDataURL() method. The image is being served to the Canvas via the URL generated from "getImageServingUrl" – Stockmon

TIL: It is crucial to set the crossOrigin attribute before setting img.src. – Feuar

It doesn't work because, in my case, the server is not sending the CORS headers. Without the crossOrigin attribute I can load the images but using it I can't – Eun

Answer 2

Just use the crossOrigin attribute and pass 'anonymous' as the second parameter

var img = new Image();
img.setAttribute('crossOrigin', 'anonymous');
img.src = url;

Fighter

To clarify, this will not work for servers that directly wont let the resource to you. That mean, that this will work only for public resources, or missconfigured servers. – Maxon

I've also had to add a timestamp to the image URL to avoid the storage server from responding with 304 without the Access-Control-Allow-Origin header. Like this img.src = url + '?' + new Date().getTime(); – Filings

didn't work for me in IE11 with images the use data-url source – Brusque

Answer 3

This method will prevent you from getting an 'Access-Control-Allow-Origin' error from the server you are accessing to.

var img = new Image();
var timestamp = new Date().getTime();
img.setAttribute('crossOrigin', 'anonymous');
img.src = url + '?' + timestamp;

Awning

Answer 4

Try the code below ...

<img crossOrigin="anonymous"
     id="imgpicture" 
     fall-back="images/penang realty,Apartment,house,condominium,terrace house,semi d,detached,
                bungalow,high end luxury properties,landed properties,gated guarded house.png" 
     ng-src="https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_272x92dp.png" 
     height="220"
     width="200"
     class="watermark">

Breakneck

what is the reason of pointless value of fall-back attribute? – Wrung

I believe the only reason this works is because of crossOrigin="anonymous" the rest is irrelevant. I'm also pretty sure ng-src is not native javascript. – Misfire

Answer 5

In my case I was using the WebBrowser control (forcing IE 11) and I could not get past the error. Switching to CefSharp which uses Chrome solved it for me.

Apologetic

Answer 6

I had the same error message. I had the file in a simple .html, when I passed the file to php in Apache it worked

html2canvas(document.querySelector('#toPrint')).then(canvas => {
            let pdf = new jsPDF('p', 'mm', 'a4');
            pdf.addImage(canvas.toDataURL('image/png'), 'PNG', 0, 0, 211, 298);
            pdf.save(filename);
        });

Barney

Answer 7

if the picture from the 3rd party site didn't set the header for cors ("access-control-allow-origin"), you can never download the picture file through chrome, even if you use the setAttribute('crossOrigin', 'anonymous'); Here are some suggestions

1. hack chrome (use an extension, this will only work on your machine)
2. proxy the image through a service running on your site. The browser will see the domain as your site. This requires your service to request the image from the 3rd party.

Gautious

Answer 8

By using fabric js we can solve this security error issue in IE.

    function getBase64FromImageUrl(URL) {
        var canvas  = new fabric.Canvas('c');
        var img = new Image();
        img.onload = function() {
            var canvas1 = document.createElement("canvas");
            canvas1.width = this.width;
            canvas1.height = this.height;
            var ctx = canvas.getContext('2d');
            ctx.drawImage(this, 0, 0);
            var dataURL = canvas.toDataURL({format: "png"});
        };
        img.src = URL;
    }

Gavriella