王者荣耀英雄攻略技巧:PHP 这个错误怎么改正，急，在线等

我的代码是
<?
//connection DataBase
$conn=mysql_connect("localhost","test","");
//open the table
mysql_select_db("image",$conn);
?>
<?
//get the form data of ID
$ID=$_POST['ID'];
$Photo=$_POST['Image'];
//check the user
$checksql="select * from image where id='$ID'";
$check_re=mysql_query($checksql,$conn);
$num=mysql_num_rows($check_re);
if($num!=0)
{
echo "此用户已在，请选择另外一个<br>";
echo "上传失败!<br>";
echo "<a href='javascript:history.back(-1)'>back</a>";
exit();
}
?>
<?
if($Photo<>"")
{
$fp=fopen($Photo,"r");
$data=addslashes(fread($fp,filesize($Photo)));
}
$sql="insert into image(id,photo) values('$ID','$data')";
mysql_query($sql,$conn) or die("插入数据失败:".mysql_error());
mysql_close($conn);
?>
错误提示是。。。
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in d:\apache\htdocs\save_image1.php on line 14
插入数据失败:No Database Selected
我应该怎么改？