getImageData cross-origin error

You can't use file:// if you're using that (Chrome allow you to override this but I won't recommend it).

For local testing use a light-weight server such as Mongoose which allow you use http://localhost as a domain to test your local pages. This way you avoid problems with CORS.

If you need to host images on a different domain you need to make sure they support cross-origin usage.

DropBox and ImgUrl (I recommend the latter for just images) both support CORS usage, but you need to request such usage by adding the crossOrigin property to your image before setting the source (or include it in the HTML tag if you're using that):

var img = new Image;

img.onload = myLoader;
img.crossOrigin = '';              ///=anonymous
img.src = 'http://imgur.com/....';

or in HTML:

<img src="..." alt="" crossOrigin="anonymous" />

Make sure you put the img.setAttribute('crossOrigin', ''); before you set the source of your image object. just like this:

var img = document.createElement("img");
//fix crossorigin here...
img.setAttribute('crossOrigin', '');
//after that put your source
img.src = imageSrcURL;
document.body.appendChild(img);