Since File API will enable access to the content of local files it is now possible to do image resize before upload (a fairly common task) without any additional te
One problem with calavera.info's answer (sorry I cannot seem to comment directly on that answer) is that the call to either CanvasRenderingContext2D.getImageData or Canvas.toDataURL mentioned in the third bullet will fail. They each throw a SECURITY_ERR: DOM Exception 18 as the image is not from the same origin or domain as the document that owns the canvas element. That seems inevitable since the image comes from the local file system (via an input type="file" tag), but the page comes from your web server.