Returning image to "browser" using snippet without img tag, just image

<?php
// PHP placeholder images
// Version: 0.1
// Author: Hinerangi Courtenay - @sky_maiden

// Usage (all parameters are optional):
// <img src="placeholder.php?size=400x150&bg=eee&fg=999&text=Generated+image" alt="Placeholder image" />

// Inspired by http://placehold.it/


// Dimensions
$getsize    = isset($_GET['size']) ? $_GET['size'] : '100x100';
$dimensions = explode('x', $getsize);

// Create image
$image      = imagecreate($dimensions[0], $dimensions[1]);

// Colours
$bg         = isset($_GET['bg']) ? $_GET['bg'] : 'ccc';
$bg         = hex2rgb($bg);
$setbg      = imagecolorallocate($image, $bg['r'], $bg['g'], $bg['b']);

$fg         = isset($_GET['fg']) ? $_GET['fg'] : '555';
$fg         = hex2rgb($fg); 
$setfg      = imagecolorallocate($image, $fg['r'], $fg['g'], $fg['b']);

// Text
 $text       = isset($_GET['text']) ? strip_tags($_GET['text']) : $getsize;
 $text       = str_replace('+', ' ', $text);

// Text positioning
$fontsize   = 4;
$fontwidth  = imagefontwidth($fontsize);    // width of a character
$fontheight = imagefontheight($fontsize);   // height of a character
$length     = strlen($text);                // number of characters
$textwidth  = $length * $fontwidth;         // text width
$xpos       = (imagesx($image) - $textwidth) / 2;
$ypos       = (imagesy($image) - $fontheight) / 2;

//imagealphablending($image, true); // setting alpha blending on
//imagesavealpha($image, true); // save alphablending setting 


// Generate text
imagestring($image, $fontsize, $xpos, $ypos, $text, $setfg);

// Render image
ob_start();
imagepng($image);
$output = ob_get_contents();
ob_end_clean();

return $output;


// Convert hex to rgb (modified from csstricks.com)
function hex2rgb($colour)
{
    $colour = preg_replace("/[^abcdef0-9]/i", "", $colour);
    if (strlen($colour) == 6)
    {
        list($r, $g, $b) = str_split($colour, 2);
        return Array("r" => hexdec($r), "g" => hexdec($g), "b" => hexdec($b));
    }
    elseif (strlen($colour) == 3)
    {
        list($r, $g, $b) = array($colour[0] . $colour[0], $colour[1] . $colour[1], $colour[2] . $colour[2]);
        return Array("r" => hexdec($r), "g" => hexdec($g), "b" => hexdec($b));    
    }
    return false;
}

?>

<img src="[[++assets_url]]components/captcha/captcha.php" alt="Captcha Image" />

    header('Content-Description: File Transfer');
    header('Content-Type: image/jpeg');
    header('Content-Transfer-Encoding: binary');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Pragma: public');
    header('Content-Length: '.filesize('cat-small.d054b748c4c9c82abc105fcc94d051791.jpg'));
    readfile('cat-small.d054b748c4c9c82abc105fcc94d051791.jpg');
    ob_end_flush

    header('Content-Description: File Transfer');
    header('Content-Type: image/png');
    header('Content-Transfer-Encoding: binary');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Pragma: public');
    
    $image = imagecreate (150, 120);
    $background = ImageColorAllocate ($image, 00, 00, 00);
    $white = ImageColorAllocate ($image, 255, 255, 255);
    ImageTTFText ($image, 18, 0, 0, 16, $white, "assets/fonts/arial.ttf", "this");
    ImagePNG($image);
    die();