Security Error with canvas.toDataURL() and drawImage()

Asked 18/2, 2012 at 22:4 Answered 20/2, 2012 at 18:56

javascript firefox google-chrome html5-canvas

<!doctype html>
<canvas id="canvas" height="200" width="200"></canvas>
<div id="new"></div>
<script>
var div = document.getElementById("new");
var canvas = document.getElementById("canvas");  
var ctx = canvas.getContext("2d");  
var img = new Image();

img.src = 'http://www.w3.org/html/logo/downloads/HTML5_Logo_512.png';
//img.src = 'local.png';

img.onload = function(){
    //draws the image on the canvas (works)
    ctx.drawImage(img,0,0,200,200);

    //creates an image from the canvas (works only for local.png)
    var sourceStr = canvas.toDataURL();

    //creates the img-tag and adds it to the div-container
    var newImage = document.createElement("img");
    newImage.src = sourceStr;
    div.appendChild(newImage);
}
</script>

This script creates a canvas with the html5-logo. From this canvas I want to create an image, using the "toDataURL()"-method. Here I get a security error.

Firefox says - Error: uncaught exception: [Exception... "Security error" code: "1000" nsresult: "0x805303e8 (NS_ERROR_DOM_SECURITY_ERR)"

Chrome says - Uncaught Error: SECURITY_ERR: DOM Exception 18

If I use the script with an image on the server it works fine. So it think this time it is really a feature and not a bug. Does anyone has an idea how I can create an image using canvas with out of an image form an other server? BTW: the error occurs if you run the site as a local file without a webserver.

Trudey answered 18/2, 2012 at 22:4 Comment(1)

Did you find an answer yet? I have the same issue, it even happens with images from the same server. Once any image has been drawn into the canvas, the whole canvas becomes inaccessible. – Tectonic 15/5, 2014 at 16:56

You are right, this is a security feature, not a bug.

If reading the Image (for instance with toDataURL or getImageData) would work, you could also read https://mail.google.com/mail/ from the context of your visitor get his emails or whatever.

Therefore, canvas elements have a origin-clean flag, which is set when external images are written to the canvas. In that case, you can no longer read from it.

You can read more about this topic here.

Appeasement answered 18/2, 2012 at 22:16 Comment(1)

The link's now broken, but I believe that information can now be found here. – Dividend 17/4, 2013 at 21:21

i believe that the error is an extension to the same origin policy, basically it isnt allowing you to manipulate a resource from another server. although insecure you could build into the server a method of retrieving external resources: myserver.com/?external=url/path/to/img... that would work in theory.

Bing answered 18/2, 2012 at 22:9 Comment(0)

Ya thats a feature. As the image is on another server. Check this

Why does canvas.toDataURL() throw a security exception?

You can catch these exceptions. But this will be headache to do for other browsers too and also not right for security.

So better solution is download that image on local.And give the image src path to that.

Quadriceps answered 20/2, 2012 at 18:56 Comment(0)

Recommended topics

Hot tags