用法：

imagecropper("图片地址", "216", "60");

会替换原图，不想替换原图自己加个参数，传入保存文件名

/**
* 图像裁剪
* @param $title string 原图路径
* @param $content string 需要裁剪的宽
* @param $encode string 需要裁剪的高
*/
function imagecropper($source_path, $target_width, $target_height)
{
	$source_info = getimagesize($source_path);
	$source_width = $source_info[0];
	$source_height = $source_info[1];
	$source_mime = $source_info['mime'];
	$source_ratio = $source_height / $source_width;
	$target_ratio = $target_height / $target_width;

	// 源图过高
	if ($source_ratio > $target_ratio)
	{
		$cropped_width = $source_width;
		$cropped_height = $source_width * $target_ratio;
		$source_x = 0;
		$source_y = ($source_height - $cropped_height) / 2;
	}
	// 源图过宽
	elseif ($source_ratio < $target_ratio)
	{
		$cropped_width = $source_height / $target_ratio;
		$cropped_height = $source_height;
		$source_x = ($source_width - $cropped_width) / 2;
		$source_y = 0;
	}
	// 源图适中
	else
	{
		$cropped_width = $source_width;
		$cropped_height = $source_height;
		$source_x = 0;
		$source_y = 0;
	}

	switch ($source_mime)
	{
	case 'image/gif':
		$source_image = imagecreatefromgif($source_path);
		break;
	case 'image/jpeg':
		$source_image = imagecreatefromjpeg($source_path);
		break;

	case 'image/png':
		$source_image = imagecreatefrompng($source_path);
		break;
	default:
		return false;
		break;
	}

	$target_image = imagecreatetruecolor($target_width, $target_height);
	$cropped_image = imagecreatetruecolor($cropped_width, $cropped_height);

	// 裁剪
	imagecopy($cropped_image, $source_image, 0, 0, $source_x, $source_y, $cropped_width, $cropped_height);
	// 缩放
	imagecopyresampled($target_image, $cropped_image, 0, 0, 0, 0, $target_width, $target_height, $cropped_width, $cropped_height);

	//保存图片到本地(两者选一)
	//$randNumber = mt_rand(00000, 99999). mt_rand(000, 999);
	//$fileName = substr(md5($randNumber), 8, 16) .".png";
	imagepng($target_image,$source_path);
	imagedestroy($target_image);

	//直接在浏览器输出图片(两者选一)
	/*
	header('Content-Type: image/jpeg');
	imagepng($target_image);
	imagedestroy($target_image);
	imagejpeg($target_image);
	imagedestroy($source_image);
	imagedestroy($target_image);
	imagedestroy($cropped_image);
	*/
}