Cross-origin data in HTML5 canvas

I'm loading an image in js and draw it into a canvas. After drawing, i retrieve imageData from the canvas:

var img = new Image();
img.onload = function() {
    canvas.drawImage(img, 0, 0);
    originalImageData = canvas.getImageData(0,0,width, height)); //chrome fails
}
img.src = 'picture.jpeg';

This works perfectly both in Safari and Firefox, but fails in Chrome with the following message:

Unable to get image data from canvas because the canvas has been tainted by cross-origin data.

The javascript file and the image are located in the same directory, so i don't understand the behavior of chorme.