ok i tested this here (http://www.pghcollectibles.com/downloads/phpimage/font/test06.php).
this is image code, file to be named number.php:
<?php
$im = imagecreate(10, 20);//this is the size of the picture width,height
$var=$_GET["number"];
$int_options = array("options"=>array("min_range"=>0, "max_range"=>9));
$number=filter_var($var, FILTER_VALIDATE_INT, $int_options);
if (!$number || $number==""){$number="0";}
$bg = imagecolorallocate($im, 255, 255, 255); //edit numbers to change background color
$black = imagecolorallocate($im, 0, 0, 0);//edit numbers to change font color
// prints first characture of $number or a 0
imagechar($im, 7, 0, 0, $number, $black);//edit 7 to change font size
header('Content-type: image/png');
imagepng($im);
?> that uses better filtering now
<?php
$var=$_GET["number"];
$int_options = array("options"=>array("min_range"=>0, "max_range"=>9));
$number=filter_var($var, FILTER_VALIDATE_INT, $int_options);
if (!$number || $number==""){$number="0";}
$back=$number-1;
$next=$number+1;
if ($number=="0"){$back="9";}
if ($number=="9"){$next="0";}
echo "<html><body><div align='center'>";
echo "<img src='number.php?number={$number}' border='0' /><br /><br />";
echo "<form method='GET'><input type='text' size='3' name='number'><br /><input type='submit' value='New Number'></form>";
echo "<br /><br />or...<br /><br />";
echo "<form method='GET'><input type='hidden' id='num' name='number' value=''><input type='submit' onclick='document.getElementById(\"num\").value=\"{$back}\"' value=' < '><input type='submit' onclick='document.getElementById(\"num\").value=\"{$next}\"' value=' > '></form>";
echo "</div></body></html>";
?>since i dont know what you want yet (i do simple stuff like this just because its fun for me to learn it and play with it) this is a sample for you to play with. using imagechar() only displays the first characture in a string but there are other functions to do for something else. it would look dumb if when you got to 10, 11, 12 etc for it to only display the 1 so i added some conditions to make the arrows loop in counting from 0-9