8 replies to this topic

[Alhazred]

I'm trying to create a capthca, I know the code that I need, I already did it in the past.
The problem is the image, I need something like this


but I don't know how to create this effect.
In the past for captcha images I used to put simple lines on the code, this time I'm trying something different.
I tried with imagefilter, but I don't see anything that could help me.
Which function do I have to use?

[ghost_x47]

GD doesn't have those functions.
You can manually do it. for ex:
1.get line from image
2.apply some sin or cos functions with random seed
3.store line to 2nd image
4.if image finished - output 2nd image.
OR
you can use imagemagick lib. They have like a dozen of distorting functions.Here the list

[bbqroast]

I have NO experience with images in PHP but I saw something where you can echo out text onto images.
How about you create a image and print letters out randomly on the Y axis.

[ghost_x47]

it's pretty easy to crack this, even if you put letters randomly - they are still letters, not distorted.

[bbqroast]

Yeah I know that...
You could just use reCaptcha- Or you could install custom fonts.
You could try making a distorted alphabet in images and have PHP put them together.
It is quite hard to do this well....

[ghost_x47]

Not neccesary.
The only problem always be -> is it profitable to hack particular defence or not. If it is - then nothing can stop hackers.)
So you only want to make hacker spent more than he will gain.
You don't actually need an absolute defence - cause it will be like..

[Alhazred]

ghost_x47 said:

GD doesn't have those functions.
You can manually do it. for ex:
1.get line from image
2.apply some sin or cos functions with random seed
3.store line to 2nd image
4.if image finished - output 2nd image.

Thanks, I've used a solution like this and it works :)

[ghost_x47]

Nice to hear that.
I never had a chance to test it.)

[Alhazred]

I was on another PC before and I hadn't the code.
Now I'm on my PC and I can post it.

<?php
session_start();

header("Content-type: image/png");

$font = "courbi.ttf";
$image = imagecreate(200,60);

$background_color = ImageColorAllocate($image, rand(0,120), rand(0,120), rand(0,120));

$colour1 = ImageColorAllocate($image, rand(120,255), rand(120,255), rand(120,255));

imagettftext($image,26,0,30,40,$colour1,$font,$_SESSION['captcha']);
imagefilter($image,IMG_FILTER_GAUSSIAN_BLUR);
$scale = 2;
$width = 200;
$height = 60;
$xperiod = 10;
$xamplitude = 5;
$yperiod = 12;
$yamplitude = 14;

// X-axis wave generation
$xp = $scale*$xperiod*rand(1,3);
$k = rand(0, 100);
for ($i = 0; $i < ($width*$scale); $i++) {
    imagecopy($image, $image,
        $i-1, sin($k+$i/$xp) * ($scale*$xamplitude),
        $i, 0, 1, $height*$scale);
}

// Y-axis wave generation
$k = rand(0, 100);
$yp = $scale*$yperiod*rand(1,2);
for ($i = 0; $i < ($height*$scale); $i++) {
    imagecopy($image, $image,
        sin($k+$i/$yp) * ($scale*$yamplitude), $i-1,
        0, $i, $width*$scale, 1);
}

imagepng($image);

imagedestroy($image);
?>

I hope that this can be useful to someone :)