通过php代码错误将图像上传到FTP

我的图像上传有问题，它不起作用。。。给我这个错误

已连接到ftp.example.com，用于用户exemple@exemple.com警告：ftp_put（）：中的文件名不能为空/home/user/public_html/foto-test.php在第26行FTP上传失败！

<?php
$ftp_server = "ftp.xxxx.com";
$ftp_user_name = "xxxx@xxxx.com";
$ftp_user_pass = "xxxxxxx";
$folder = "/public_html/images";
$destination_file = $folder . $_FILES['file']['name'];
$source_file = $_FILE['file']['tmp_name'];
// set up basic connection
$conn_id = ftp_connect($ftp_server);
ftp_pasv($conn_id, true); 
// login with username and password
$login_result = ftp_login($conn_id, $ftp_user_name, $ftp_user_pass); 
// check connection
if ((!$conn_id) || (!$login_result)) { 
    echo "FTP connection has failed!";
    echo "Attempted to connect to $ftp_server for user $ftp_user_name"; 
    exit; 
} else {
    echo "Connected to $ftp_server, for user $ftp_user_name";
}
// upload the file
$upload = ftp_put($conn_id, $destination_file, $source_file, FTP_BINARY); //line 26
// check upload status
if (!$upload) { 
echo "FTP upload has failed!";
} else {
echo "Uploaded $source_file to $ftp_server as $destination_file";
}
// close the FTP stream 
ftp_close($conn_id);
?>

我试图更改$folder目标，但它给了我一些错误。。。