captcha_non_gd.php

这些都是我以前学习是用到的源码

	* of the given length adding the relevant crc
	*/
	function png_chunk($length, $type, $data)
	{
		$raw = $type . $data;

		return pack('N', $length) . $raw . pack('N', crc32($raw));
	}

	/**
	* Creates greyscale 8bit png - The PNG spec can be found at
	* http://www.libpng.org/pub/png/spec/PNG-Contents.html we use
	* png because it's a fully recognised open standard and supported
	* by practically all modern browsers and OSs
	*/
	function create_png($raw_image, $width, $height)
	{
		// SIG
		$image = pack('C8', 137, 80, 78, 71, 13, 10, 26, 10);

		// IHDR
		$raw = pack('N2', $width, $height);
		$raw .= pack('C5', 8, 0, 0, 0, 0);
		$image .= $this->png_chunk(13, 'IHDR', $raw);

		// IDAT
		if (@extension_loaded('zlib'))
		{
			$raw_image = gzcompress($raw_image);
			$length = strlen($raw_image);
		}
		else
		{
			// The total length of this image, uncompressed, is just a calculation of pixels
			$length = ($width + 1) * $height;

			// Adler-32 hash generation
			// Note: The hash is _backwards_ so we must reverse it

			if (@extension_loaded('hash'))
			{
				$adler_hash = strrev(hash('adler32', $raw_image, true));
			}
			else if (@extension_loaded('mhash'))
			{
				$adler_hash = strrev(mhash(MHASH_ADLER32, $raw_image));
			}
			else
			{
				// Optimized Adler-32 loop ported from the GNU Classpath project
				$temp_length = $length;
				$s1 = 1;
				$s2 = $index = 0;

				while ($temp_length > 0)
				{
					// We can defer the modulo operation:
					// s1 maximally grows from 65521 to 65521 + 255 * 3800
					// s2 maximally grows by 3800 * median(s1) = 2090079800 < 2^31
					$substract_value = ($temp_length < 3800) ? $temp_length : 3800;
					$temp_length -= $substract_value;

					while (--$substract_value >= 0)
					{
						$s1 += ord($raw_image[$index]);
						$s2 += $s1;

						$index++;
					}