Due to browser restrictions around <canvas> element, all images loaded into pixie need to be either hosted on the same domain as pixie or cross-domain enabled, otherwise you will receive Could not export canvas with external image error when trying to download or export image or apply certain operations like crop or merge.
If your image is cross-origin enabled, you also need to enable cross-origin functionality in pixie via crossOrigin option.
var pixie = new Pixie({
crossOrigin: true
});