Database add a new field "qr_exist" tynyint(1) in tbl_user_master. (1 mean already got QR code).

Then upload "phpqrcode" zip file to Controller folder and extract the zip file.
https://www.dropbox.com/s/1sn68ln2c5fahdk/phpqrcode.zip?dl=0
Note : this "phpqrcode" folder must saved in the same directory as your code file.

Then add this code at top of page :
include 'phpqrcode/qrlib.php';

Then add this code to create QR code image : $invitation_url = site_url("register/index/".$first_acc_code); $path = $_SERVER['DOCUMENT_ROOT']; $file = $path.'/uploads/qrimages/'.$first_acc_code.".png"; $ecc = 'L'; $pixel_Size = 10; $frame_Size = 10; QRcode::png($invitation_url, $file, $ecc, $pixel_Size, $frame_Size);

Then show QR code image by code below : <center><img src="<?=base_url()?>uploads/qrimages/<?=$unique_code?>.png"></center>