Plupload is JavaScript API for building file uploaders. It supports multiple file selection, file filtering, chunked upload, client side image downsizing and when necessary can fallback to alternative runtimes, like Flash and Silverlight.
if "preserve_headers" set TRUE, the image uploaded to server side, and the orientation in exif info exists but the image has already be adjusted. So, the server side can not readjust again, but can only get and remove exif info.
if "preserve_headers" set FALSE, it will call the function "_rotateToOrientaion" to adjust it, but this is WRONG! the image has already being adjusted!