Get QString data from the QPixmap

[Cobra91151]

Hi! I want to get QString data from QPixmap image which was constructed by loadFromData function.

connect(netManager, &QNetworkAccessManager::finished, [this](QNetworkReply *reply) {
           QByteArray data = reply->readAll();
           QPixmap captchaPixmap;
           captchaPixmap.loadFromData(data);
           qDebug() << data;
}

It's a captcha from the website, from PHP script it has header("Content-type: image/gif"); So it returns image, also I have the captcha code but it is stored in a $_SESSION global variable. I can't parse this $_SESSION variable from C++ because header("Content-type: image/gif"); loads only images.

I want to compare captcha data and user input.

Any ideas how to do it? Thanks.

[SGaist]

Hi,

You don't want to QString if you want to access images data. QString as its name suggest is for manipulating strings.

If you want to manipulate the data from the image you should rather use QImage and then you can access the underlying bytes through QImage::bits.

Out of curiosity, why not use something like recaptcha ?

[Cobra91151]

@SGaist

I will try it. Thanks.

[Cobra91151]

@SGaist

I have checked your solution, but how to translate those bits to QString or something to compare with the user input. I have tried different solutions but it failed. Thanks.

[SGaist]

Do you mean you want to extract the text the user has input stored in the gif ?

[Cobra91151]

@SGaist

No, I want extract it to compare with user input from QLineEdit text function.

So for example, the captcha code: ABCD.
User input: ABCD.
So I can compare it as text or some hash to validate if it matches.

qDebug() << data.bits(); // it returns 0xa1ff200

[SGaist]

QImage::bits gives you the starting address of the raw image data.

Where do you get that gif from ?

[Cobra91151]

@SGaist

I parse it from my website.

Here is the some PHP code:

$_SESSION["image"] = implode('', $cod);  // gets code captcha
header("Content-type: image/gif"); 		//loads the captcha image
imagegif($src); 
imagedestroy($src);

I need this - $_SESSION["image"] = implode('', $cod); to be parsed so I can compare later with user input.
I use $_SESSION["image"] to validate captcha code on the website. So I need to parse it to the application but since the header content type is the image, I can't access the captcha code.

Another solution is to use this project from GitHub:
QtCaptcha

Also I can port PHP captcha generation to the C++ but it will take long.

[SGaist]

What are you using to generate that captcha ?

[Cobra91151]

@SGaist

I generate it by PHP code.

Image:

[SGaist]

So basically, you want to decipher the captcha image you generate client side to check whether the use input is correct ?

[Cobra91151]

@SGaist

Yes.

[SGaist]

You do realise that the goal of the captcha is to make it really difficult for computer to deduce what's on it ?

[Cobra91151]

@SGaist

Yes, I know it. I think I have the idea how to decipher it. I will try it and reply.

[Cobra91151]

@SGaist

So my solution is:

I have stored $_SESSION["image"] value to the txt file witch is the captcha code. Then I read this file and now get the value to compare with the user input. Also I'm thinking about putting it to the database or restrict access to the file.

[SGaist]

By the way, why do it on the client side ?