دلیل کار نکردن imagecreatefromjpeg ?

function saveImage($keyword,$usedPath,$Id,$newWidth,$newHeight){
    $file=$_FILES[$keyword]['tmp_name']; // a address of first location for file after upload
    $ext=fetchImgExt($keyword);
    $originalPath = getcwd() . "/" . $usedPath . "/original/" . $Id . $ext;
    copy($file, $originalPath);

    if($ext=='.jpeg'){$ext='.jpg';}
    $thumbPath = getcwd() . "/" . $usedPath . "/" . $Id . $ext;

    resizeImage($originalPath,$newWidth,$newHeight,$thumbPath);
}





function fetchImgExt($imgPostKey) {
    $ext = $_FILES[$imgPostKey]['type']; // extension of file. example : image/png image/jpg ...
    $ext = str_replace('image/', '.', $ext);
    return $ext;
}





function resizeImage($sourcePath,$newWidth,$newHeight=null,$destination) {

    $parts = explode(".", $sourcePath);
    $ext = $parts[count($parts) - 1];

    if ($ext == 'png') {
        $sourceImage = imagecreatefrompng($sourcePath);
    }

    if ($ext == 'jpeg') {
        $sourceImage = imagecreatefromjpeg($sourcePath);
    }

    list($srcWidth, $srcHeight) = getimagesize($sourcePath);
    $ratio = getImageRatio($sourcePath);

    if ($newWidth == 0) {
        $newWidth = $newHeight / $ratio;
    }

    if ($newHeight == 0) {
        $newHeight = $newWidth * $ratio;
    }

    $destinationImage = imagecreatetruecolor($newWidth, $newHeight);
    imagecopyresampled($destinationImage, $sourceImage, 0, 0, 0, 0, $newWidth, $newHeight, $srcWidth, $srcHeight);


    if ($destination == null) {
        header("Content-Type: image/jpeg");

        if ($ext == 'png') {
            imagepng($destinationImage, null, 9);
        }

        if ($ext == 'jpeg') {
            imagejpeg($destinationImage, null, 100);
        }


    } else {
        if ($ext == 'png') {
            imagepng($destinationImage, $destination,9);
        }

        if ($ext == 'jpeg') {
            imagejpeg($destinationImage, $destination,100);
        }

    }

}





function getImageRatio($sourcePath){
    list($width,$height)=getimagesize($sourcePath);
    $imageRatio=$height/$width;
    return $imageRatio;
}