php verification code not showing on screen

Reasons and solutions for the PHP verification code not being displayed:

1. If it is utf-8, it is possible that the BOM has not been cleared

2. There is output before Header("Content-type: image/PNG");

3. The first line of PHP hides code, such as spaces, carriage returns, etc.

Solution code:

$image_width=70;           //设置图像宽度
$image_height=18;       //设置图像高度
$new_number=$_GET[num];
//$new_number=5;
$num_image=imagecreate($image_width,$image_height); //创建一个画布
imagecolorallocate($num_image,255,255,255);    //设置画布的颜色
$black=imagecolorallocate($num_image,0,0,0);
/**/for($i=0;$i
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