CAPTCHA image do not show – fix here available

[Anonymous]

When I use placeholder #_CAPTCHA in reservation form, GD lib generate image, but image wont show in browser.

Please, fix it by code bellow.

To fix this bug, do this:

eme_functions.php

function eme_captcha_generate() {
…
// give image back
ob_clean(); // <—- BUG FIX
header (“Content-type: image/gif”);
imagegif($im);
imagedestroy($im);
exit;
}

[Franky]

Why would ob_clean be needed there?

[Anonymous]

In my case, if there is not ob_clean function, header or any other data are sent, before GD lib generate captcha image and source link has invalid content. Web browser show only small black square, no captcha code. Probably, there is some colision between this and other plugin.

[Franky]

Well, I don’t use ob_start anywhere, so ob_clean is not something I’d need here as well.
Indeed either another plugin (or your theme with empty lines) might be responsible, and that should be corrected.

[Anonymous]

Sorry, error in my wordpress template.

response of server was:
77u/<image data>

77u/ is UTF8 BOM identification.

I use czech language, edit some teplate files and save in format UTF8 with BOM!

To fix this I use Notepad++, choose menu-format-convert to UTF8 (without BOM)
In status bar of app was shown: ANSI as UTF8

This working properly

[Anonymous]

I had to insert the ob_clean to have the captcha displayed.
If I call directly the
[URL]/?eme_captcha=generate&f=49a075d52a3fb455454ff957861c54511a3e5392587712&ts=1638664168

I receive a 0x0 gif image when I dont use the ob_clean

How to find where the incorrect char (or blank line) is added?

Thanks,
Stephan

[Anonymous]

OK, I found my problem:
Analysing the GIF returned by the script, I saw the GIF begin with “\xef bb bf”, the gif should begin with “GIF”. So there are 3 hex chars before the file.
This is the BOM encoding for UTF8, it means that a file is encoded in “UTF8 with BOM”.

Searched through all my files with
grep -R $’\UFEFF’ | grep php

The wp-config.php was the culprit. Problem solved.
Ref: https://www.herongyang.com/Unicode/Notepad-Byte-Order-Mark-BOM-FEFF-EFBBBF.html

[Franky]

Yes, I make sure the theme isn’t responsible for captcha generation errors, but if the issue was in wp-config.php then many things that create images on the fly would not have worked.

[Author]

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