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CAPTCHAs are used to prevent automated software from performing actions which degrade the quality of a service of a given system, whether due to abuse or resource expenditure. Creates a CAPTCHA image in PHP, which displays 5 numbers. The code is stored in a session variable ... then, the user must enter the code correctly. Can be used on registration forms, login forms, etc.
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<?php
session_start();
header('Content-type: image/png');
$im = imagecreate(180, 70);
$lcolor1 = imagecolorallocate($im, 0,0,0);
$lcolor2 = imagecolorallocate($im, rand(0,70),rand(0, 70),rand(0, 70));
$bgcolor2 = imagecolorallocate($im, rand(200, 255),rand(200, 255),rand(200, 255));
$_SESSION['code'] = str_replace('7', '1', rand(10000, 99999));
$id = $_SESSION['code'];
imagefill($im, 0, 0, $bgcolor2);
$end1 = rand(0, 100);
imagefilledrectangle($im, 0, 0, $end1, 70, ImageColorAllocate($im, rand(235, 255),rand(235, 255),rand(235, 255)));
$end2 = $end1+rand(0, 100);
imagefilledrectangle($im, $end1, 0, $end2, 70, ImageColorAllocate($im, rand(235, 255),rand(235, 255),rand(235, 255)));
$end3 = $end2+rand(0, 100);
imagefilledrectangle($im, $end2, 0, $end3, 70, ImageColorAllocate($im, rand(235, 255),rand(235, 255),rand(235, 255)));
imagefilledrectangle($im, $end3, 0, 180, 70, ImageColorAllocate($im, rand(235, 255),rand(235, 255),rand(235, 255)));
$y1 = rand(25, 50);
ImageTTFText ($im, rand(17, 20), rand(-30, 30), rand(10, 20), $y1, $lcolor1, 'fonts/verdana.ttf', substr($id, 0, 1));
$y2 = rand(25, 50);
ImageTTFText ($im, rand(17, 20), rand(0, 30), rand(45, 55), $y2, $lcolor2, 'fonts/trebuc.ttf', substr($id, 1, 1));
$y3 = rand(25, 50);
ImageTTFText ($im, rand(17, 25), rand(-20, 0), rand(80, 90), $y3, $lcolor1, 'fonts/trebuc.ttf', substr($id, 2, 1));
$y4 = rand(25, 50);
ImageTTFText ($im, rand(16, 25), rand(0, 30), rand(115, 125), $y4, $lcolor1, 'fonts/verdana.ttf', substr($id, 3, 1));
$y5 = rand(25, 50);
ImageTTFText ($im, rand(18, 20), rand(-25, 0), rand(150, 160), $y5, $lcolor2, 'fonts/trebuc.ttf', substr($id, 4, 1));
$x = rand(0, 50);
$y = rand(0, 50);
imagepng($im);
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