我在做壹個PHP驗證碼圖片的時候無論我把($im,0,0,0); 這三個0改成什麽數背景總是黑色，為什麽呢？代碼如下

用我的代碼吧

<?php

/*實現驗證碼圖片*/

session_start();

//1、創建壹個畫布

$image=imagecreate(100,40);

//2、定義顏色

$background=imagecolorallocate($image,200,255,255);//背景顏色

$text_color=imagecolorallocate($image,255,125,125);//字體顏色

$yansucolor=imagecolorallocate($image,255,0,0);//雪花顏色

//3、為畫布填充顏色

imagefill($image,0,0,$background);

//4、往畫布添加幹擾素

for($i=1;$i<rand(100,200);$i++)

{

$x=rand(0,90);

$y=rand(0,40); //添加雪花

imagesetpixel($image,$x,$y,$yansucolor);

}

//添加線段

imageline($image,20,0,80,10,$yansucolor);

imageline($image,0,0,80,40,$yansucolor);

imageline($image,0,20,40,40,$yansucolor);

//5、往畫布填充內容

$arr=array("A","B",9,"C","D","E","F",3,"G","H","I","J","K",8,"L","M","N","O",1,"P","Q","R","S","T","U",2,"V","W","X","Y","Z","a","b",7,"c","d","e","f","g",4,"h","i","j","k","l","m","n","o","p","q",6,"r","s","t","u","v",5,"w","x","y","z",0);

for($j=0;$j<6;$j++)

{

$num=rand(0,15);

$str=$str.$arr[$num];

}

$_SESSION[yzm]=$str;

$angle=rand(0,20);//傾斜角度

imagettftext($image,20,$angel,10,30,$text_color,"Greek_i.ttf",$str);

//$num=rand(1000,9999);

//向系統聲明

header("Content-type:image/png");

//將php文件轉換為圖片

imagepng($image);

//釋放資源

imagedestroy($image);