$result = move_uploaded_file($tmpName, $filePath);
$orig_image = imagecreatefromjpeg($filePath);
$image_info = getimagesize($filePath);
$width_orig  = $image_info[0]; // current width as found in image file
$height_orig = $image_info[1]; // current height as found in image file
$width = 1024; // new image width
$height = 768; // new image height
$destination_image = imagecreatetruecolor($width, $height);
imagecopyresampled($destination_image, $orig_image, 0, 0, 0, 0, $width, $height, $width_orig, $height_orig);
// This will just copy the new image over the original at the same filePath.
imagejpeg($destination_image, $filePath, 100);