Thinking about accessibility for visually impaired users when they need to fill out the contact form. We decided to implement the eSpeak NG library, which has the functionality to speak captcha characters.

Example

header('Content-Type: audio/wav');
header('Content-Disposition: inline;filename=captcha.wave');

echo (new Espeak())
        ->setOption('stdout')
        ->setOption('s', '110')
        ->setOption('v', (new Espeak())->getVoiceCode($_SERVER['HTTP_ACCEPT_LANGUAGE']))
        ->execute('Hello World');

Library Documentation

https://github.com/espeak-ng/espeak-ng