A quick function to automatically generate a multi line image from a string, with the image size automatically calculated from the string itself.

<?php

function multilineimage($string){

    // Probably not the best way of handling newlines, but bar OS9, doesn't really cause a problem
    $string = str_replace("\r","",$string);
    $string = explode("\n",$string);

    $maxlen = 0;
    foreach ($string as $str){
        if (strlen($str) > $maxlen){
            $maxlen = strlen($str);
        }
    }

    // Set font size
    $font_size = 4;

    // Create image width dependant on width of the string
    $width  = imagefontwidth($font_size)*$maxlen;
    // Set height to that of the font
    $height = imagefontheight($font_size) * count($string);
    // Create the image pallette
    $img = imagecreate($width,$height);
    // Grey background
    $bg    = imagecolorallocate($img, 205, 255, 255);
    // White font color
    $color = imagecolorallocate($img, 0, 0, 0);

    $ypos = 0;

    foreach ($string as $str){

        $len = strlen($str);
        for($i=0;$i<$len;$i++){
            // Position of the character horizontally
            $xpos = $i * imagefontwidth($font_size);
            // Draw character
            imagechar($img, $font_size, $xpos, $ypos, $str, $color);
            // Remove character from string
            $str = substr($str, 1);   
        }
        $ypos = $ypos + imagefontheight($font_size);   
    }

    // Return the image 
    header("Content-Type: image/gif");
    imagegif($img);
    // Remove image
    imagedestroy($img);
}

multilineimage("This is an image
This is line 2\nLine 3
Line 4");

?>