The newest version of this script allows for variable line heights, centered text, drop shadows, background images, and more.
Here is an example:

The script is included here on this page, below.

The original article is here.

Note: This script requires NetPBM and ImageMagick installed on the server for drop shadows to work.

header_image.php PHP Source

The following is the source for the image creation script.  To use it, call it in an HTML page like so:

<?php
// image_header.php
// Generate dynamic text banner images using TTF fonts and PHP.
// Copyright 2003,2004  The Johns Hopkins University, All rights reserved.
// Author:  Jeffrey D. Silverman
// Date:    14-January-2004
// Description:
// Use this script to generate graphic headers.
// Pass in a value for "$text" to print.
// Example usage:
//    <img src='header_image.php?text=this%20is%20the%20text' width='300' height='23'>
//
// CONFIGURATION - Change these items manually here or pass in values via the URL
// ITEMS that can be passed in (optionally) via the URL are:
// fontdir
// bg_b
// bgcolor
// bg_g
// bgimage
// bg_r
// center_x
// center_y
// cols
// drop_shadow
// fg_b
// fgcolor
// fg_g
// fg_r
// font
// fontdir
// image_height
// image_width
// lineheight
// linewidth
// shadow_offset_x
// shadow_offset_y
// text
// x
// y
define("fontdir", "." ); // Important! This MUST be a real directory for the script to work!
define("font",   "arial.ttf" ); // Important! This MUST be a real TTF or PostScript font file for the script to work!
define("TEMP_IMAGE_DIR",   "header_image_temp" );

define("image_width",   100 );
define("image_height",   23 );
define("lineheight",   12 );
define("x",   10 );
define("y",   lineheight );
define("cols",   1 );
// Text (foreground) color, RGB values 0-255
define("fg_r",   0 );
define("fg_g",   0 );
define("fg_b",   0 );
// Background color, RGB values 0-255
define("bg_r",   255 );
define("bg_g",   255 );
define("bg_b",   255 );

# Configuration of external programs
# You MUST put the full path to the proper programs here. Not doing so will disable
# the drop-shadow functionality
define("GDTOPNG", "/usr/local/bin/gdtopng");
define("MOGRIFY", "/usr/bin/mogrify");
// END OF CONFIGURATION

// DO NOT CHANGE BELOW THIS LINE //////////////////////////

if (! is_dir(TEMP_IMAGE_DIR) ) mkdir(TEMP_IMAGE_DIR);

// Check for saved images based on MD5 Hash of the $_SERVER['QUERY_STRING']
$saved_image = TEMP_IMAGE_DIR . "/" . md5($_SERVER['QUERY_STRING']) . ".png";
if (is_file( $saved_image)){
    header("Content-type: image/png");
    echo file_get_contents($saved_image);
    exit;
} else {
    $fontdir = $_REQUEST['fontdir'] ? $_REQUEST['fontdir'] : fontdir;
    $font = $_REQUEST['font'] ? $_REQUEST['font'] : font;
    $image_width = $_REQUEST['image_width'] ? $_REQUEST['image_width'] : image_width;
    $image_height = $_REQUEST['image_height'] ? $_REQUEST['image_height'] : image_height;
    $lineheight = $_REQUEST['lineheight'] ? $_REQUEST['lineheight'] : lineheight;
    $x = $_REQUEST['x'] ? $_REQUEST['x'] : x;
    // $y = $_REQUEST['y'] ? $_REQUEST['y'] : $_REQUEST['lineheight'] ? $_REQUEST['lineheight'] : lineheight;
    $y = $_REQUEST['y'] ? $_REQUEST['y'] : y;
    if ($_REQUEST['center_x']){
        // x-offset = ((width of box) - (width of string)) / 2
        $x = ( $image_width / 2 ) + ($image_height / 2 );
    }
    // Need to make this dynamic.  Not all header images should break on multiple lines! (Notably the page_title)
    if ($_REQUEST['linewidth']){
        // linewidth MUST be passed in through the URL to split long lines.
        // Otherwise the text will be all on one line.
        $split_lines = preg_split("/(.{" . $_REQUEST['linewidth'] . "}\S*)\s/", $_REQUEST['text'], -1, PREG_SPLIT_DELIM_CAPTURE);
    } else {
        $split_lines = array($_REQUEST['text']);
    }

    $cols = $_REQUEST['cols'] ? $_REQUEST['cols'] : cols;
    // Text color, RGB values 0-255
    $fg_r = $_REQUEST['fg_r'] ? $_REQUEST['fg_r'] : fg_r;
    $fg_g = $_REQUEST['fg_g'] ? $_REQUEST['fg_g'] : fg_g;
    $fg_b = $_REQUEST['fg_b'] ? $_REQUEST['fg_b'] : fg_b;
    // background color, RGB values 0-255
    $bg_r = $_REQUEST['bg_r'] ? $_REQUEST['bg_r'] : bg_r;
    $bg_g = $_REQUEST['bg_g'] ? $_REQUEST['bg_g'] : bg_g;
    $bg_b = $_REQUEST['bg_b'] ? $_REQUEST['bg_b'] : bg_b;
    // Background Image
    $fgcolor = $_REQUEST['fgcolor'] ? $_REQUEST['fgcolor'] : false;
    $bgcolor = $_REQUEST['bgcolor'] ? $_REQUEST['bgcolor'] : false;
    $bgimage = $_REQUEST['bgimage'] ? $_REQUEST['bgimage'] : false;
    // Sample colors...
    // $white = imagecolorallocate($im, 255, 255, 255);
    // $gray1 = imagecolorallocate($im, 204, 204, 204);
    // $white = imagecolorallocate($im, 255, 255, 255);
    // $orange = imagecolorallocate($im, 220, 210, 60);
    // $dark_red = imagecolorallocate($im, 130, 28, 28);
    // $black = imagecolorallocate($im, 0, 0, 0);

    $filetypes = array(
                        "gif" => "gif"
                      , "jpg" => "jpeg"
                      , "jpeg" => "jpeg"
                      , "jpe" => "jpeg"
                      , "png" => "png"
                      );

    // TO DEBUG. Set Content-tpye to text/plain
    // header("Content-type: text/html");
    header("Content-type: image/png");
    if ($fgcolor) {
        $fgcolor = preg_replace("/[^0-9A-Za-z]/", "", $fgcolor);
        list($fg_r, $fg_g, $fg_b) = array(hexdec( substr($fgcolor, 0, 2) ),
                hexdec( substr($fgcolor, 2, 2) ),
                hexdec( substr($fgcolor, 4, 2) ));
    }
    if ($bgcolor) {
        $bgcolor = preg_replace("/[^0-9A-Za-z]/", "", $bgcolor);
        list($bg_r, $bg_g, $bg_b) = array(hexdec( substr($bgcolor, 0, 2) ),
                hexdec( substr($bgcolor, 2, 2) ),
                hexdec( substr($bgcolor, 4, 2) ));
    }
    // Hack/Bugfix:
    $result = preg_replace("/&amp;/", "&", $_REQUEST['text']); // fixes problem with &amp; showing up inside images!

    foreach ($split_lines as $line){
        if (! preg_match("/^\s*$/", $line)) $lines[] = $line;
    }
    $no_lines = count($lines);
    if ($_REQUEST['center_y']){
        $center_offset = ($no_lines + 1);
        $y = ($image_height / 2 ) - ( (($no_lines / 2) * $lineheight) - $lineheight );
    }


    // $lines = preg_split("/\n/", $result);
    $result = preg_replace("/\n/", "\r\n", $result);
    $im = imagecreate($image_width, $image_height);
    $im_shadow = imagecreate($image_width, $image_height);

    if (is_file($bgimage)){
        $suffix = array_pop(split("\.", $bgimage));
        $func = "imagecreatefrom" . $filetypes[$suffix];
        $im2 = $func($bgimage);
        imagecopyresized($im, $im2, 0, 0, 0, 0, 1, 1, 1, 1);
    }


    $background = imagecolorallocate($im, $bg_r, $bg_g, $bg_b);
    $black = imagecolorallocate($im, 0, 0, 0);
    $textcolor = imagecolorallocate($im, $fg_r, $fg_g, $fg_b);

    if ($_REQUEST['drop_shadow'] == 1 and (defined("GDTOPNG") and defined("MOGRIFY"))){
        $y_orig = $y;
        $shadow_offset_x = isset($_REQUEST['shadow_offset_x']) ? $_REQUEST['shadow_offset_x'] : 2;
        $shadow_offset_y = isset($_REQUEST['shadow_offset_y']) ? $_REQUEST['shadow_offset_y'] : 2;
        foreach ($lines as $string) {
            $string = preg_replace("/^\s*/", "", $string);
            imagefttext($im, $lineheight - 1, 0, $x+$shadow_offset_x, $y+$shadow_offset_y, $black, "$fontdir/$font",  $string, array() );
            $y += $lineheight;
        }
        $y = $y_orig;
        $tempimage = md5(time() . "" . rand(0,10000000));

        imagegd($im, "/tmp/$tempimage.gd");
        system(GDTOPNG . " /tmp/$tempimage.gd /tmp/$tempimage.png");
        system(MOGRIFY . " -blur 2 /tmp/$tempimage.png");
        $im = imagecreatefrompng("/tmp/$tempimage.mgk");
        unlink("/tmp/$tempimage.png");
        unlink("/tmp/$tempimage.gd");
        unlink("/tmp/$tempimage.mgk");

        $textcolor = imagecolorallocate($im, $fg_r, $fg_g, $fg_b);
        foreach ($lines as $string) {
            $string = preg_replace("/^\s*/", "", $string);
            imagefttext($im, $lineheight - 1, 0, $x, $y, $textcolor, "$fontdir/$font",  $string, array() );
            $y += $lineheight;
        }
    } else {
        foreach ($lines as $string) {
            $string = preg_replace("/^\s*/", "", $string);
            imagefttext($im, $lineheight - 1, 0, $x, $y, $textcolor, "$fontdir/$font",  $string, array() );
            $y += $lineheight;
        }
    }
    imagepng($im);
    imagepng($im, $saved_image);
    imagedestroy($im);
}
?>