关键：当参数名为"@绝对路径"，这时 CURL 會幫你做 multipart/form-data 編碼
实现方法：
$params = array(
'file' => '@/Pictures/753161072647248225.jpg',
'file_1' => '@/Pictures/753161072647248225.jpg',
'file_2' => '@/Pictures/753161072647248225.jpg',
); $ch = curl_init();
curl_setopt( $ch, CURLOPT_URL, $url );
curl_setopt( $ch, CURLOPT_RETURNTRANSFER, 1 );
curl_setopt( $ch, CURLOPT_POST, true );
curl_setopt( $ch, CURLOPT_POSTFIELDS, $params );
$response = curl_exec($ch);