Implementation of PHP verification code function

/**

*Generate verification code image

*/

public function actionVerfiycode() {

Header ( "Content-type: image/gif" );

$border = 0; //Whether you want a border 1 yes: 0 no

$how = 4; //Verification code digits

$w = $how * 15; //Picture width

$h = 20; //Picture height

$fontsize = 5; //Font size

$alpha = "abcdefghijkmnopqrstuvwxyz"; //Verification code content 1: letters

$number = "0123456789"; //Verification code content 2: numbers

$randcode = ""; //Verification code string initialization

srand ( ( double ) microtime () * 1000000 ); //Initialize random number seed

$im = ImageCreate ( $w, $h ); //Create verification image

$bgcolor = ImageColorAllocate ( $im, 255, 255, 255 ); //Set the background color

ImageFill ( $im, 0, 0, $bgcolor ); // Fill the background color

if ($border) {

$black = ImageColorAllocate ( $im, 0, 0, 0 ); //Set the border color

ImageRectangle ( $im, 0, 0, $w - 1, $h - 1, $black ); //Draw the border

}

for($i = 0; $ i < $how; $i ++) {

$alpha_or_number = mt_rand (0, 1); //Letters or numbers

$str = $alpha_or_number ? $alpha : $number;

$which = mt_rand ( 0, strlen ( $str ) - 1 ); // Which character to take

$code = substr ( $str, $which, 1 ); // Take the character

$j = ! $i ? 4 : $j + 15; //Draw character position

$color3 = ImageColorAllocate ( $im, mt_rand ( 0, 100 ), mt_rand ( 0, 100 ), mt_rand ( 0, 100 ) ); // Character color will be drawn

ImageChar ( $im , $fontsize, $j, 3, $code, $color3 ); //Draw characters

$randcode .= $code; //Add the verification code string bit by bit

}

for($i = 0; $i < 5; $i ++) //Draw background interference lines

{

$color1 = ImageColorAllocate ( $im, mt_rand ( 0, 255 ), mt_rand ( 0, 255 ), mt_rand ( 0, 255 ) ); //Interference line color

ImageArc ( $im, mt_rand ( - 5, $w ), mt_rand ( - 5, $h ), mt_rand ( 20, 300 ), mt_rand ( 20, 200 ), 55, 44, $color1 ); //Interference line

}

for($i = 0; $i < $how * 40; $i ++) //Draw background interference points

{

$color2 = ImageColorAllocate ( $im, mt_rand ( 0, 255 ), mt_rand ( 0, 255 ), mt_rand ( 0, 255 ) ); //Interference point color

ImageSetPixel ( $im, mt_rand ( 0, $w ), mt_rand ( 0 , $h ), $color2 ); //Interference point

}

$session=new CHttpSession;

$session->open();

Yii::app()->session-> add('randcode',$randcode);

/*End of drawing*/

Imagegif ($im);

ImageDestroy ($im);

/*End of drawing*/

}