Hi everyone.

`imagerotate()` php function fails to return an image object, at least with PHPv7.4 on my hosting.

More specifically, the error occurs specifying 180 degrees as the parameter value (so half of the times the captcha will not be displayed, as designed in function `generate_image()`).

I'm not sure, but I think I remember getting similar errors in the past with older versions of PHP, for some other particular values (negative?). Has anyone else experience similar issues with `imagerotate()`? And what about PHP8?

I have temporally avoided this issue manually changing the value to 179.9 for the parameter. But if It's a common issue, maybe a fix can be added for it: it could be verified that the value returned by `imagerotate()` is not `false`; or a option in the admin panel to not rotate the captcha background?

Best regards.