新浪微博SDK图片上传方法：

<?php

function build_http_query_multi($params) {
		if (!$params) return '';

		uksort($params, 'strcmp');

		$pairs = array();

		$boundary = uniqid('------------------');
		$MPboundary = '--'.$boundary;
		$endMPboundary = $MPboundary. '--';
		$multipartbody = '';

		foreach ($params as $parameter => $value) {

			if( in_array($parameter, array('pic', 'image')) && $value{0} == '@' ) {
				$url = ltrim( $value, '@' );
				$content = file_get_contents( $url );
				$array = explode( '?', basename( $url ) );
				$filename = $array[0];

				$multipartbody .= $MPboundary . "\r\n";
				$multipartbody .= 'Content-Disposition: form-data; name="' . $parameter . '"; filename="' . $filename . '"'. "\r\n";
				$multipartbody .= "Content-Type: image/unknown\r\n\r\n";
				$multipartbody .= $content. "\r\n";
			} else {
				$multipartbody .= $MPboundary . "\r\n";
				$multipartbody .= 'content-disposition: form-data; name="' . $parameter . "\"\r\n\r\n";
				$multipartbody .= $value."\r\n";
			}

		}

		$multipartbody .= $endMPboundary;
		return $multipartbody;
}

另一种方法：

<?php

$ch = curl_init();
//加@符号,curl就会进行文件上传处理
$data = array('img'=>'@'. dirname(__FILE__).'/image.jpg');
curl_setopt($ch,CURLOPT_URL,"http://localhost/upload.php");
curl_setopt($ch,CURLOPT_RETURNTRANSFER,true);
curl_setopt($ch,CURLOPT_POST,true);
curl_setopt($ch,CURLOPT_POSTFIELDS,$data);
$result = curl_exec($ch);
curl_close($ch);