captcha_non_gd.php

这些都是我以前学习是用到的源码

			if ($i > $offset_y && $i < $offset_y + $img_height)
			{
				for ($j = 0; $j < $offset_x; $j++)
				{
					$image .= chr(mt_rand(140, 255));
				}

				for ($j = 0; $j < $code_len; $j++)
				{
					$image .= $this->randomise(substr($hold_chars[$code{$j}][$i - $offset_y - 1], 1), $char_widths[$j]);
				}

				for ($j = $offset_x + $img_width; $j < $this->width; $j++)
				{
					$image .= chr(mt_rand(140, 255));
				}
			}
			else
			{
				for ($j = 0; $j < $this->width; $j++)
				{
					$image .= chr(mt_rand(140, 255));
				}
			}
		}
		unset($hold_chars);

		$image = $this->create_png($image, $this->width, $this->height);

		// Output image
		header('Content-Type: image/png');
		header('Cache-control: no-cache, no-store');
		echo $image;
		exit;
	}

	/**
	* This is designed to randomise the pixels of the image data within
	* certain limits so as to keep it readable. It also varies the image
	* width a little
	*/
	function randomise($scanline, $width)
	{
		$new_line = '';

		$end = strlen($scanline) - ceil($width/2);
		for ($i = floor($width/2); $i < $end; $i++)
		{
			$pixel = ord($scanline{$i});

			if ($pixel < 190)
			{
				$new_line .= chr(mt_rand(0, 205));
			}
			else if ($pixel > 190)
			{
				$new_line .= chr(mt_rand(145, 255));
			}
			else
			{
				$new_line .= $scanline{$i};
			}
		}

		return $new_line;
	}

	/**
	* This creates a chunk of the given type, with the given data