Generate Verification Code in PHP

Beginner web, is trying to write a blog, registration needs to use the verification code. I have learned the book head first in the code, changed the Chinese comments, put on

<?PHPSession_Start(); //defining the Important constants    Define(' Captcha_numchars ', 6); Define(' Captcha_width ', 100); Define(' Captcha_height ', 25); //generate a phrase    $pass _phrase="";  for($i= 0;$i<CAPTCHA_NUMCHARS;$i++)    {        $pass _phrase.=CHR(Mt_rand(97,122)); }    //stored in the session    $_session[' Pass_phrase ']=SHA1($pass _phrase); //Create an image    $img=imagecreatetruecolor (Captcha_width,captcha_height); //set white background black text gray pattern    $BG _color=imagecolorallocate ($img, 255,255,255); $text _color=imagecolorallocate ($img, 0,0,0); $graphic _color=imagecolorallocate ($img, 64,64,64); //Fill BackgroundImagefilledrectangle ($img, 0,0,captcha_width,captcha_height,$BG _color); //draw some random lines.     for($i= 0;$i<3;$i++) {Imageline ($img, 0,Rand()%captcha_height,captcha_width,Rand()%captcha_height,$graphic _color); }    //draw a few random points     for($i= 0;$i<50;$i++) {Imagesetpixel ($img,Rand()%captcha_width,Rand()%captcha_height,$graphic _color); }    //draw a phraseImagettftext ($img, 18,0,5,captcha_height-5,$text _color, "Courier New Bold.ttf",$pass _phrase); //creating PNG images    Header("Content-type:image/png"); Imagepng ($img); //Clear CacheImagedestroy ($img);?>

The basic idea is to use the GD library to create an image, and then randomly draw lines, dots, and characters. The use of the function can be found, here is no longer to repeat, to say a few questions I encountered.

1. After opening the above page, the browser display picture does not load correctly, Baidu provides a solution, is to add the Ob_clean ( ) function before the header () function, clear the cache, and then successfully opened.

2. Open after the image does not have a verification code, suspected Imagettftext () function of the problem, but did not solve, in the online search to find someone else about the code, the Imagettftext () function is replaced by imagestring (), So the show was successful.

Here again put another person's code, the effect is better than the book, posted in Baidu know on the question, should not say I tort it = =

<?PHPSession_Start();//Create random Code for($i= 0;$i<4;$i++){    $_nmsg.=Dechex(Mt_rand(0, 15));}//save it in the session.$_session[' Code '] =$_nmsg;//Long and high$_width= 75;$_height= 25;//Create an image$_img= Imagecreatetruecolor ($_width,$_height);$_white= Imagecolorallocate ($_img, 255, 255, 255); Imagefill ($_img, 0, 0,$_white);//Create a black border$_black= Imagecolorallocate ($_img, 100, 100, 100); Imagerectangle ($_img, 0, 0,$_width-1,$_height-1,$_black);//Random Dash Bar for($i= 0;$i<6;$i++) {$_rnd_color= Imagecolorallocate ($_img,Mt_rand(0,255),Mt_rand(0,255),Mt_rand(0,255)); Imageline ($_img,Mt_rand(0,75),Mt_rand(0,25),Mt_rand(0,75),Mt_rand(0,25),$_rnd_color);}//randomly hit snowflakes for($i= 1;$i<100;$i++) {imagestring ($_img, 1,Mt_rand(1,$_width),Mt_rand(1,$_height),"*",Imagecolorallocate ($_img,Mt_rand(200,255),Mt_rand(200,255),Mt_rand(200,255)));}//Output Verification Code for($i= 0;$i<strlen($_session[' Code ']);$i++) {imagestring ($_img,Mt_rand(3,5),$i*$_width/4+Mt_rand(1,10),Mt_rand(1,$_height/2),$_session[' Code '] [$i],Imagecolorallocate ($_img,Mt_rand(0,150),Mt_rand(0,100),Mt_rand(0,150)));}//Output ImageOb_clean(); Header(' Content-type:image/png '); Imagepng ($_img);//destroyedImagedestroy ($_img);?>

Generate Verification Code in PHP