Captcha renders as broken text instead of image using PHP & GD - php

Question

I am using this Kohana Captcha module in an application. The image renders correctly on my local environment but on our dev environment it returns the following:
�PNG
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This is the render() method:
public function render($html = TRUE)
{
// Creates $this->image
$this->image_create(Captcha::$config['background']);
// Add a random gradient
if (empty(Captcha::$config['background']))
{
$color1 = imagecolorallocate($this->image, mt_rand(200, 255), mt_rand(200, 255), mt_rand(150, 255));
$color2 = imagecolorallocate($this->image, mt_rand(200, 255), mt_rand(200, 255), mt_rand(150, 255));
$this->image_gradient($color1, $color2);
}
// Add a few random lines
for ($i = 0, $count = mt_rand(5, Captcha::$config['complexity'] * 4); $i < $count; $i++)
{
$color = imagecolorallocatealpha($this->image, mt_rand(0, 255), mt_rand(0, 255), mt_rand(100, 255), mt_rand(50, 120));
imageline($this->image, mt_rand(0, Captcha::$config['width']), 0, mt_rand(0, Captcha::$config['width']), Captcha::$config['height'], $color);
}
// Calculate character font-size and spacing
$default_size = min(Captcha::$config['width'], Captcha::$config['height'] * 2) / (utf8::strlen($this->response) + 1);
$spacing = (int) (Captcha::$config['width'] * 0.9 / utf8::strlen($this->response));
// Draw each Captcha character with varying attributes
for ($i = 0, $strlen = utf8::strlen($this->response); $i < $strlen; $i++)
{
// Use different fonts if available
$font = Captcha::$config['fontpath'].Captcha::$config['fonts'][array_rand(Captcha::$config['fonts'])];
// Allocate random color, size and rotation attributes to text
$color = imagecolorallocate($this->image, mt_rand(0, 150), mt_rand(0, 150), mt_rand(0, 150));
$angle = mt_rand(-40, 20);
// Scale the character size on image height
$size = $default_size / 10 * mt_rand(8, 12);
$box = imageftbbox($size, $angle, $font, utf8::substr($this->response, $i, 1));
// Calculate character starting coordinates
$x = $spacing / 4 + $i * $spacing;
$y = Captcha::$config['height'] / 2 + ($box[2] - $box[5]) / 4;
// Write text character to image
imagefttext($this->image, $size, $angle, $x, $y, $color, $font, utf8::substr($this->response, $i, 1));
}
// Output
return $this->image_render($html);
}
and the image_render()
/**
* Returns the img html element or outputs the image to the browser.
*
* #param boolean $html Output as HTML
* #return mixed HTML, string or void
*/
public function image_render($html)
{
// Output html element
if ($html === TRUE)
return '<img src="'.url::site('captcha/'.Captcha::$config['group']).'" width="'.Captcha::$config['width'].'" height="'.Captcha::$config['height'].'" alt="Captcha" class="captcha" />';
// Send the correct HTTP header
Request::current()->headers('Content-Type', 'image/'.$this->image_type)
->headers('Cache-Control', 'no-store, no-cache, must-revalidate, post-check=0, pre-check=0')
->headers('Pragma', 'no-cache')
->headers('Connection', 'close');
// Pick the correct output function
$function = 'image'.$this->image_type;
$function($this->image);
// Free up resources
imagedestroy($this->image);
}
GD library is enabled on the dev environment. Both environments use apache 2.2, php 5.4. Is there another server setting I need to enable?

Answer 1

This type of bugs sometimes bugs me, try to add:
die();
after the last line:
return $this->image_render($html);
Sometimes it works for me.

Answer 2

The text looks like a PNG datastream, only rendered by a text editor instead of an image viewer.