Use recaptcha by Google. It is more good and better then mybb default captcha.
i want to solve this problem i have no google captcha keys .
I really recommend using a registration question instead because captchas are annoying for users to deal with. Sometimes even I have issues figuring out letters. Good questions are ones that relate to your forum's niche so you have a legit user who is interested.
You are right but why captchas are not shown ?
^ you are using a free web host and we cannot easily say why something is not working (without checking)
There are several line breaks at the beginning of the HTML source that shouldn't be there. However I can't tell you where they come from.
i have checked this problem is due to a pluging because i have disabled all the plugins now working . How i fix it ?
I gave you a link to a solution above... My guess is that it's caused by the BAM plugin which has a .php file with wrong encoding, IIRC.