Most likely this is caused by scanning the license using the "Black & White" setting instead of "Grayscale."  If the license looks incorrect in the preview window, click the "Delete Page" button in the top right.  Click "Scan Page" again to rescan the license.  Make sure that "Grayscale" is selected, and that the DPI is 100.  If you are still getting black streaks after selecting "Grayscale," the scanner may need to be cleaned (see the Related Link below for details).