Fatal error: Call to undefined function curl_init()

<?php $filename = "xx.gif"; $handle = fopen($filename, "r"); $data = fread($handle, filesize($filename)); // $data is file data $pvars = array('image' => base64_encode($data), 'key' => IMGUR_API_KEY); $timeout = 30; $curl = curl_init(); curl_setopt($curl, CURLOPT_URL, 'http://api.imgur.com/2/upload.xml'); curl_setopt($curl, CURLOPT_TIMEOUT, $timeout); curl_setopt($curl, CURLOPT_POST, 1); curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1); curl_setopt($curl, CURLOPT_POSTFIELDS, $pvars); $xml = curl_exec($curl); curl_close ($curl); var_dump($xml); ?> I'm playing with the Imgur API, but it doesn't seems to work. PHP.net says that `curl_init()` is in PHP5, but my host says it isn't. How can I make this work?