/**
* Generate noisy background
*
* @param int $width: width of the image in pixels
* @param int $height: width of the image in pixels
* @param string $word: the captcha word
* @param string $backgroundType (see constants)
* @param array $backgroundImages: array of background image file names
* @param boolean $morphBackground: if TRUE, the background will be morphed
* @param boolean $blurBackground: if TRUE, the background will be blurred
* @return string GD image identifier of noisy background
*/
public static function generateNoisyBackground($width, $height, $word, $backgroundType, $backgroundImages = array(), $morphBackground = TRUE, $blurBackground = TRUE)
{
$image = ImageCreateTrueColor($width, $height);
if ($backgroundType != self::BACKGROUND_TYPE_TRANSPARENT) {
// Generate noisy background, to be merged with CAPTCHA later
// any suggestions on how best to do this much appreciated
// sample code would be even better!
// I'm not an OCR expert (hell, I'm not even an image expert; puremango.co.uk was designed in MsPaint)
// so the noise models are based around my -guesswork- as to what would make it hard for an OCR prog
// ideally, the character obfuscation would be strong enough not to need additional background noise
// in any case, I hope at least one of the options given here provide some extra security!
$tempBackground = ImageCreateTrueColor($width * 1.5, $height * 1.5);
$background = ImageColorAllocate($image, 255, 255, 255);
ImageFill($image, 0, 0, $background);
$tempBackgroundColor = ImageColorAllocate($tempBackground, 255, 255, 255);
ImageFill($tempBackground, 0, 0, $tempBackgroundColor);
// We draw all noise onto tempBackground
// then if we're morphing, merge from tempBackground to image
// or if not, just copy a $width x $height portion of $tempBackground to $image
// tempBackground is much larger so that when morphing, the edges retain the noise.
switch ($backgroundType) {
case self::BACKGROUND_TYPE_WHITE_WITH_GRID:
// Draw grid on x
for ($i = RandomContentUtility::getRandomNumberInRange(6, 20); $i < $width * 2; $i += RandomContentUtility::getRandomNumberInRange(10, 25)) {
ImageSetThickness($tempBackground, RandomContentUtility::getRandomNumberInRange(2, 6));
$textColor = RandomContentUtility::getRandomColor(100, 150);
$textColor2 = ImageColorAllocate($tempBackground, $textColor[0], $textColor[1], $textColor[2]);
ImageLine($tempBackground, $i, 0, $i, $height * 2, $textColor2);
}
// Draw grid on y
for ($i = RandomContentUtility::getRandomNumberInRange(6, 20); $i < $height * 2; $i += RandomContentUtility::getRandomNumberInRange(10, 25)) {
ImageSetThickness($tempBackground, RandomContentUtility::getRandomNumberInRange(2, 6));
$textColor = RandomContentUtility::getRandomColor(100, 150);
$textColor2 = ImageColorAllocate($tempBackground, $textColor[0], $textColor[1], $textColor[2]);
ImageLine($tempBackground, 0, $i, $width * 2, $i, $textColor2);
}
break;
case self::BACKGROUND_TYPE_WHITE_WITH_SQUIGGLES:
ImageSetThickness($tempBackground, 4);
for ($i = 0; $i < strlen($word) + 1; $i++) {
$textColor = RandomContentUtility::getRandomColor(100, 150);
$textColor2 = ImageColorAllocate($tempBackground, $textColor[0], $textColor[1], $textColor[2]);
$points = array();
// Draw random squiggle for each character
// the longer the loop, the more complex the squiggle
// keep random so OCR can't say "if found shape has 10 points, ignore it"
// each squiggle will, however, be a closed shape, so OCR could try to find
// line terminations and start from there. (I don't think they're that advanced yet..)
for ($j = 1; $j < RandomContentUtility::getRandomNumberInRange(5, 10); $j++) {
$points[] = RandomContentUtility::getRandomNumberInRange(1 * (20 * ($i + 1)), 1 * (50 * ($i + 1)));
$points[] = RandomContentUtility::getRandomNumberInRange(30, $height + 30);
}
ImagePolygon($tempBackground, $points, intval(sizeof($points) / 2), $textColor2);
}
break;
case self::BACKGROUND_TYPE_MORPHED_IMAGE_BLOCKS:
// Take random chunks of $backgroundImages and paste them onto the background
for ($i = 0; $i < sizeof($backgroundImages); $i++) {
// Read each image and its size
$tempImages[$i] = ImageCreateFromJPEG(GeneralUtility::getFileAbsFileName($backgroundImages[$i]));
$tempWidths[$i] = imagesx($tempImages[$i]);
$tempHeights[$i] = imagesy($tempImages[$i]);
}
$blocksize = RandomContentUtility::getRandomNumberInRange(20, 60);
for ($i = 0; $i < $width * 2; $i += $blocksize) {
// Could randomise blocksize here... hardly matters
for ($j = 0; $j < $height * 2; $j += $blocksize) {
$imageIndex = RandomContentUtility::getRandomNumberInRange(0, sizeof($tempImages) - 1);
$cut_x = RandomContentUtility::getRandomNumberInRange(0, $tempWidths[$imageIndex] - $blocksize);
$cut_y = RandomContentUtility::getRandomNumberInRange(0, $tempHeights[$imageIndex] - $blocksize);
ImageCopy($tempBackground, $tempImages[$imageIndex], $i, $j, $cut_x, $cut_y, $blocksize, $blocksize);
}
}
// Cleanup
for ($i = 0; $i < sizeof($tempImages); $i++) {
ImageDestroy($tempImages[$i]);
}
break;
}
if ($morphBackground) {
// Morph background
// We do this separately to the main text morph because:
// a) the main text morph is done char-by-char, this is done across whole image
// b) if an attacker could un-morph the background, it would un-morph the CAPTCHA
// hence background is morphed differently to text
// why do we morph it at all? it might make it harder for an attacker to remove the background
// morph_chunk 1 looks better but takes longer
// this is a different and less perfect morph than the one we do on the CAPTCHA
// occasonally you get some dark background showing through around the edges
// it doesn't need to be perfect as it's only the background.
$morph_chunk = RandomContentUtility::getRandomNumberInRange(1, 5);
$morph_y = 0;
for ($x = 0; $x < $width; $x += $morph_chunk) {
$morph_chunk = RandomContentUtility::getRandomNumberInRange(1, 5);
$morph_y += RandomContentUtility::getRandomNumberInRange(-1, 1);
ImageCopy($image, $tempBackground, $x, 0, $x + 30, 30 + $morph_y, $morph_chunk, $height * 2);
}
ImageCopy($tempBackground, $image, 0, 0, 0, 0, $width, $height);
$morph_x = 0;
for ($y = 0; $y <= $height; $y += $morph_chunk) {
$morph_chunk = RandomContentUtility::getRandomNumberInRange(1, 5);
$morph_x += RandomContentUtility::getRandomNumberInRange(-1, 1);
ImageCopy($image, $tempBackground, $morph_x, $y, 0, $y, $width, $morph_chunk);
}
} else {
// Just copy tempBackground onto $image
ImageCopy($image, $tempBackground, 0, 0, 30, 30, $width, $height);
}
// Cleanup
ImageDestroy($tempBackground);
if ($blurBackground) {
$image = self::blurImage($image);
}
}
return $image;
}
