$bar_w = 100;
$max_y = 300;
$margin_top = 20;
$margin_bottom = 20;
$margin_left = 20;
$margin_right = 20;
$y_div = 10;
$rects = array();

$last_x2 = $margin_left;
$i = 1;
$pt = "pt".$i;
while (isset($_GET[$pt])) {
	$x1 = $last_x2 + 1;
	$x2 = $x1 + $bar_w;
	$y1 = $margin_top + $max_y - $_GET[$pt];
	$y2 = $margin_top + $max_y;
	$ar = array($x1, $y1, $x2, $y2);
	array_push($rects, $ar);
	$i++;
	$last_x2 = $x2;
	$pt = "pt".$i;
}
$img_w = $last_x2 + $margin_right;
$img_h = $margin_top + $max_y + $margin_bottom;

$ih = imagecreate($img_w, $img_h);

$black = imagecolorallocate($ih, 0, 0, 0);
$white = imagecolorallocate($ih, 255, 255, 255);

imagefill($ih, 0, 0, $white);
for ($r = 0; $r < count($rects); $r++) {
	$red = rand(0, 255);
	$green = rand(0, 255);
	$blue = rand(0, 255);
	$hist_color = imagecolorallocate($ih, $red, $green, $blue);
	imagefilledrectangle($ih, $rects[$r][0], $rects[$r][1], $rects[$r][2], $rects[$r][3], $hist_color);
	imageline($ih, $rects[$r][2], $margin_top + $max_y, $rects[$r][2], $margin_top + $max_y + 3, $black);
	$ttfbox = imagettfbbox(8, 0, 'c:\winnt\fonts\arial.ttf', "pt" . ($r + 1));
	$half_pt = ($bar_w/2) - ceil(($ttfbox[4] - $ttfbox[6])/2);
	imagettftext($ih, 8, 0, $rects[$r][0] + $half_pt, $rects[$r][3] + 10, $black, 'c:\winnt\fonts\arial.ttf', "pt" . ($r + 1));
} 

imageline($ih, $margin_left, $margin_top, $margin_left, $margin_top + $max_y + 3, $black);
imageline($ih, $margin_left, $margin_top + $max_y, $last_x2, $margin_top + $max_y, $black);
$tick = 0;
while ($tick < $max_y) {
	$tick += $y_div;
	$tick_y = $margin_top + $max_y - $tick;
	imageline($ih, $margin_left - 3, $tick_y, $margin_left, $tick_y, $black);
}

imagepng($ih);
imagedestroy($ih);