Php website background construction (verification code) error, please help modify

Php website background construction (verification code) error, please help modify I want to determine whether the entered verification code is consistent with the verification code on the image, $ _ SESSION ['code'] is the image verification code, and number is (!
) How can I modify the verification code entered in the text box?

The program is as follows. I guess the problem lies in the sentence if ($ _ POST ['Number'] ==$ _ SESSION ['code ']).
Header ("Content-type: text/html; charset = gb2312"); // sets the file encoding format
Class chkinput {
Var $ name;
Var $ pwd;

Function chkinput ($ x, $ y)
{
$ This-> name = $ x;
$ This-> pwd = $ y;
}

Function checkinput ()
{
Include ("../conn. php ");
$ SQL = mysql_query ("select * from tb_admin where name = '". $ this-> name. "'", $ conn );
$ Info = mysql_fetch_array ($ SQL );
If ($ info = false)
{
Echo"