PHP create an image with custom text, background and foreground colors

PHP code:-
<?php
header("Content-Type: image/png");
$size = NULL;
$x = NULL;
$height = NULL;
$y = NULL;
/* $fonts = array("font.ttf", "font bd.ttf");
  shuffle($fonts);
  $font = $fonts[0]; */
$font = "font.ttf";
if (!isset($_GET["favicon"]) && !isset($_GET['image-min'])) {
    $width = NULL;
    if (isset($_GET["width"]))
        $width = $_GET["width"];
    if ($width > 920) {
        $size = 100;
        $height = 110;
    } elseif ($width < 920 && $width > 750) {
        $size = 50;
        $height = 60;
    } elseif ($width < 750 && $width > 550) {
        $size = 30;
        $height = 40;
    } else {
        $size = 30;
        $height = 40;
    }
    $im = imagecreate($width, $height);
} elseif (isset($_GET['favicon'])) {
    $im = imagecreate(16, 16);
    $text = "Z";
    $size = 15;
} elseif (isset($_GET['image-min'])) {
    $width = NULL;
    $height = NULL;
    if (isset($_GET['width']))
        $width = $_GET['width'];
    if (isset($_GET['height']))
        $height = $_GET['height'];
    $im = imagecreate($width, $height);
    $size = 20;
    if (isset($_GET['size']))
        $size = $_GET['size'];
}
if (!isset($_POST['get'])) {
    if (isset($_REQUEST['text'])) {
        $text = $_REQUEST['text'];
    } else {
        $text = "Z U C K N E T";
    }
    $br = 46;
    $bg = 49;
    $bb = 146;
    $tr = 0;
    $tg = 0;
    $tb = 0;
    if (isset($_GET['br']) && isset($_GET['bg']) && isset($_GET['bb'])) {
        $br = $_GET['br'];
        $bg = $_GET['bg'];
        $bb = $_GET['bb'];
    }
    if (isset($_GET['tr']) && isset($_GET['tg']) && isset($_GET['tb'])) {
        $tr = $_GET['tr'];
        $tg = $_GET['tg'];
        $tb = $_GET['tb'];
    }
    $background = imagecolorallocate($im, $br, $bg, $bb);
    $textclr = imagecolorallocate($im, $tr, $tg, $tb);
    $bbox = imagettfbbox($size, 0, $font, $text);
    $x = $bbox[0] + (imagesx($im) / 2) - ($bbox[4] / 2);
    $y = $bbox[1] + (imagesy($im) / 2) - ($bbox[5] / 2);
    imagettftext($im, $size, 0, $x, $y, $textclr, $font, strtolower($text));
    imagepng($im);
    imagedestroy($im);
} else {
    echo $height;
}
?>

Using with <img>:-
<img src="logo.php?logo-min&width=500&height=200&size=48&br=51&bg=51&bb=51&tr=255&tg=255&tb=255"/>