[Hỏi] Code kiểm tra và mã hóa input

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<div class="center">Tên truy nhập<br/><input name="nick" maxlength="32" value=""/><br/>Mật khẩu (bao gồm chữ và số, chú ý: không đặt mật khẩu dễ đoán như: 123456,adgjm,abcdef,vv.. )<br/><input name="pass" maxlength="32" value=""/><br/>E-mail (dùng để lấy lại mật khẩu bị quên, vidu: cc@gmail.com)<br/><input name="email" maxlength="100" value=""/><br/>Giới tính<br/><select name="sex"><option value="1">Nam</option><option value="2">Nữ</option></select><br/><img src="users-captcha.php?55baec9085b54" alt="Captcha"/><br/>Nhập mã ở hình trên vào đây:<br/><input name="captcha" maxlength="6"/><br/><br/><input type="submit" value="Đăng ký"/></div></form><div class="center">
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