I suspect you haven't configured your development box to display PHP error messages. You are defining a constant that is not a valid identifier:
define('localhost/samp/sample2/uploads', 'images/');
That means that you cannot use it directly:
$file = localhost/samp/sample2/uploads . uniqid() . '.png';
... should be triggering:
Notice: Use of undefined constant localhost - assumed 'localhost'
Notice: Use of undefined constant samp - assumed 'samp'
Warning: Division by zero
Notice: Use of undefined constant sample2
Warning: Division by zero
Notice: Use of undefined constant uploads - assumed 'uploads'
Warning: Division by zero
... and file
will only contain the base file name (e.g. 53676a01cdb59.png
) but not path component. You need to use this syntax:
$file = constant('localhost/samp/sample2/uploads') . uniqid() . '.png';
... or, even better, give the constant a sensible name:
define('DIR_UPLOADS', 'images/');