How download images from ftp I imported products with the help of feeds via commerce product processor. The images from http://example.com/image.jpg downloaded successfully.  But why does not loading the images from ftp://account:123@xx.xxx.xxx.xxx/image.jpg ?
Because the image actually does not below at /image.jpg. You need to investigate where you are storing your files at admin/config/media/file-system. And from there you might find where is your files locate.

The default file path is going to be /sites/default/files so it might be ftp://account:123@xx.xxx.xxx.xxx/sites/default/filesimage.jpg.