PHP文件作为图像源不起作用（HTML，PHP）

Question

My php file creates a png image. The image is ready and is saved into the given folder, but cannot load it on the page (it just show the place of the image, but empty).

This is the "captcha_image.php":

<?php
    $dirPath="/opt/lampp/htdocs/WebSiteFolder/dfxCaptcha/";
    $font='/opt/lampp/htdocs/WebSiteFolder/DejaVuSerif-Bold.ttf';
    $imgWidth=200;
    $imgHeight=50;        
    global $image;
    $image = imagecreatetruecolor($imgWidth, $imgHeight) or die("Cannot initialize a new GD image stream.");
    $background_color = imagecolorallocate($image, 0, 0, 0);
    $text_color = imagecolorallocate($image, 255, 255, 255);    
    imagefilledrectangle($image, 0, 0, $imgWidth, $imgHeight, $background_color);    
    $letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';    
    $len = strlen($letters);
    $letter = $letters[rand(0, $len - 1)];
    $word = "";    
    for ($i = 0; $i < 4; $i++) {
        $letter = $letters[rand(0, $len - 1)];         
        imagettftext($image, 15, 0, $i*50+25, 50, $text_color, $font, $letter);
        $word .= $letter;
    }
    $_SESSION['captcha_string'] = $word;
    $images = glob($dirPath."*.png");
    foreach ($images as $image_to_delete) {
        @unlink($image_to_delete);
    }
    header ("Content-type: image/png");
    imagepng($image, $dirPath."image" . time() . ".png");
?>

I use this in the HTML:

<img src="includes/captcha_image.php" id="captcha">

How can I display the image to the page?

Answer 1

Your captcha_image.php file doesn't output the file to the browser, because you gave two arguments to the imagepng function.

The documentation says:

to

The path or an open stream resource (which is automatically being closed after this function returns) to save the file to. If not set or NULL, the raw image stream will be outputted directly.

You probably want to specify no second argument – this will mean the image is not saved, however. You did not show us your logic for accepting CAPTCHAs, but it seems to involve session management, in which case you don't need to save the file.

This should be your last line:

imagepng($image);

Additionally, please consider using an existing CAPTCHA solution. What you are doing with your code produces clear text, which is extremely readable to OCR bots nowadays. Depending on the purpose of your project you might even get away with no CAPTCHA (e.g. for comments on blog articles you can specify hidden form fields, then use a spam filter). If a CAPTCHA is truly crucial, you will need a better solution than what you have.