<?php namespace App\Http\Controllers\Auth;
Remove the white space before your php tag starts
This thread seems to be talking about the same issue - it sounds like this error is usually caused by having some data sent out of the server before the namespace statement is encountered.
Could your web hosting be inserting some code into your page before the PHP code?
Is there a UTF-8 Byte Order Mark at the beginning of the document?
On the other hand, it could also be a bug in ImageUploader... the main PHP file puts the namespace after the class definition, which I haven't seen in the PHP documentation, which says it should be the very first PHP code. From this page