该程序是不用GD库可以生成当前时间的PNG格式图象，给人大开眼界，很有参考价值. teaman整理

<?php

function set_4pixel($r, $g, $b, $x, $y)
{
global $sx, $sy, $pixels;

$ofs = 3 * ($sx * $y + $x);
$pixels[$ofs] = chr($r);
$pixels[$ofs + 1] = chr($g);
$pixels[$ofs + 2] = chr($b);
$pixels[$ofs + 3] = chr($r);
$pixels[$ofs + 4] = chr($g);
$pixels[$ofs + 5] = chr($b);
$ofs += 3 * $sx;
$pixels[$ofs] = chr($r);
$pixels[$ofs + 1] = chr($g);
$pixels[$ofs + 2] = chr($b);
$pixels[$ofs + 3] = chr($r);
$pixels[$ofs + 4] = chr($g);
$pixels[$ofs + 5] = chr($b);
}
//生成数字图象的函数
function draw2digits($x, $y, $number)
{
draw_digit($x, $y, (int) ($number / 10));
draw_digit($x + 11, $y, $number % 10);
}

function draw_digit($x, $y, $digit)
{
global $sx, $sy, $pixels, $digits, $lines;

$digit = $digits[$digit];
$m = 8;
for ($b = 1, $i = 0; $i < 7; $i++, $b *= 2) {
if (($b & $digit) == $b) {
$j = $i * 4;
$x0 = $lines[$j] * $m + $x;
$y0 = $lines[$j + 1] * $m + $y;
$x1 = $lines[$j + 2] * $m + $x;
$y1 = $lines[$j + 3] * $m + $y;
if ($x0 == $x1) {
$ofs = 3 * ($sx * $y0 + $x0);
for ($h = $y0; $h <= $y1; $h++, $ofs += 3 * $sx) {
$pixels[$ofs] = chr(0);
$pixels[$ofs + 1] = chr(0);
$pixels[$ofs + 2] = chr(0);
}
} else {
$ofs = 3 * ($sx * $y0 + $x0);
for ($w = $x0; $w <= $x1; $w++) {
$pixels[$ofs++] = chr(0);
$pixels[$ofs++] = chr(0);
$pixels[$ofs++] = chr(0);
}
}
}
}
}

//将文字加入到图象中
function add_chunk($type)
{
global $result, $data, $chunk, $crc_table;

// chunk :为层
// length: 4 字节: 用来计算 chunk
// chunk type: 4 字节
// chunk data: length bytes
// CRC: 4 字节: 循环冗余码校验

// copy data and create CRC checksum
$len = strlen($data);
$chunk = pack("c*", ($len >> 24) & 255,
($len >> 16) & 255,
($len >> 8) & 255,
$len & 255);
$chunk .= $type;
$chunk .= $data;

// calculate a CRC checksum with the bytes chunk[4..len-1]
$z = 16777215;
$z |= 255 << 24;
$c = $z;
for ($n = 4; $n < strlen($chunk); $n++) {
$c8 = ($c >> 8) & 0xffffff;
$c = $crc_table[($c ^ ord($chunk][$n])) & 0xff] ^ $c8;
}
$crc = $c ^ $z;

$chunk .= chr(($crc >> 24) & 255);
$chunk .= chr(($crc >> 16) & 255);
$chunk .= chr(($crc >> 8) & 255);
$chunk .= chr($crc & 255);

// 将结果加到$result中
$result .= $chunk;
}


//主程序

$sx = 80;
$sy = 21;
$pixels = "";

// 填充
for ($h = 0; $h < $sy; $h++) {
for ($w = 0; $w < $sx; $w++) {
$r = 100 / $sx * $w + 155;
$g = 100 / $sy * $h + 155;
$b = 255 - (100 / ($sx + $sy) * ($w + $h));
$pixels .= chr($r);
$pixels .= chr($g);
$pixels .= chr($b);
}
}

$date = getdate();
$s = $date["seconds"];
$m = $date["minutes"];
$h = $date["hours"];
$digits = array(95, 5, 118, 117, 45, 121, 123, 69, 127, 125);
$lines = array(1, 1, 1, 2, 0, 1, 0, 2, 1, 0, 1, 1, 0, 0, 0, 1, 0, 2, 1, 2, 0, 1, 1, 1, 0, 0, 1, 0);

draw2digits(4, 2, $h);
draw2digits(30, 2, $m);
draw2digits(56, 2, $s);
set_4pixel(0, 0, 0, 26, 7);
set_4pixel(0, 0, 0, 26, 13);
set_4pixel(0, 0, 0, 52, 7);
set_4pixel(0, 0, 0, 52, 13);

// 创建循环冗余码校验表
$z = -306674912; // = 0xedb88320
for ($n = 0; $n < 256; $n++) {
$c = $n;
for ($k = 0; $k < 8; $k++) {
$c2 = ($c >> 1) & 0x7fffffff;
if ($c & 1) $c = $z ^ ($c2); else $c = $c2;
}
$crc_table[$n] = $c;
}

// PNG file signature
$result = pack("c*", 137,80,78,71,13,10,26,10);

// IHDR chunk data:
// width: 4 bytes
// height: 4 bytes
// bit depth: 1 byte (8 bits per RGB value)
// color type: 1 byte (2 = RGB)
// compression method: 1 byte (0 = deflate/inflate)
// filter method: 1 byte (0 = adaptive filtering)
// interlace method: 1 byte (0 = no interlace)
$data = pack("c*", ($sx >> 24) & 255,
($sx >> 16) & 255,
($sx >> 8) & 255,
$sx & 255,
($sy >> 24) & 255,
($sy >> 16) & 255,
($sy >> 8) & 255,
$sy & 255,
8,
2,
0,
0,
0);
add_chunk("IHDR");

// 以下不敢乱翻译，请自行参考
// scanline:
// filter byte: 0 = none
// RGB bytes for the line
// the scanline is compressed with "zlib", method 8 (RFC-1950):
// compression method/flags code: 1 byte ($78 = method 8, 32k window)
// additional flags/check bits: 1 byte ($01: FCHECK = 1, FDICT = 0, FLEVEL = 0)
// compressed data blocks: n bytes
// one block (RFC-1951):
// bit 0: BFINAL: 1 for the last block
// bit 1 and 2: BTYPE: 0 for no compression
// next 2 bytes: LEN (LSB first)
// next 2 bytes: one's complement of LEN
// LEN bytes uncompressed data
// check value: 4 bytes (Adler-32 checksum of the uncompressed data)
//
$len = ($sx * 3 + 1) * $sy;
$data = pack("c*", 0x78, 0x01,
1,
$len & 255,
($len >> 8) & 255,
255 - ($len & 255),
255 - (($len >> 8) & 255));
$start = strlen($data);
$i2 = 0;
for ($h = 0; $h < $sy; $h++) {
$data .= chr(0);
for ($w = 0; $w < $sx * 3; $w++) {
$data .= $pixels[$i2++];
}
}


// calculate a Adler32 checksum with the bytes data[start..len-1]
$s1 = 1;
$s2 = 0;
for ($n = $start; $n < strlen($data); $n++) {
$s1 = ($s1 + ord($data[$n])) % 65521;
$s2 = ($s2 + $s1) % 65521;
}
$adler = ($s2 << 16) | $s1;

$data .= chr(($adler >> 24) & 255);
$data .= chr(($adler >> 16) & 255);
$data .= chr(($adler >> 8) & 255);
$data .= chr($adler & 255);
add_chunk("IDAT");

// IEND: marks the end of the PNG-file
$data = "";
add_chunk("IEND");

// 列印图象

echo($result);
?>

//如何调用，其实很简单，将上面存为Timeimg.php
//然后新建一个页面如下：

<html>
<head>
<title>test</title>
<meta http-equiv="Content-Type" content="text/html">
</head>
<body>
<img src="Timeimg.php"> //以图象连接方式调用PHP文件
</body>
</html>