After drawing an image from a different domain onto a canvas, you can no longer access its ImageData object because of the same-origin-policy. I was having a tough fight with this problem for a few days, to find out that the YQL returns DATA URIs!! So, here's a sample of extracting the edge of an image from a different domain, using YQL. (Playing around with Twitter icons may be interesting...) --
![YQL利用外部ドメイン画像処理 Cross-domain image-processing using YQL - jsdo.it - Share JavaScript, HTML5 and CSS](https://cdn-ak-scissors.b.st-hatena.com/image/square/61fb62b19e4cfb39330f1a78db74450f44f8c57d/height=288;version=1;width=512/http%3A%2F%2Fjsdo-static-contents.s3.amazonaws.com%2Fimages%2Fcapture%2Fv%2FC%2F7%2FvC7z.jpg%3Ft%3D1297173546)