[eluser]Jhourlad Estrella[/eluser]
This kind of workaround requires directly altering the CAPTHA Helper code, which is, of course, not advisable. But if you really need to specify your own font size, open core/helpers/captcha_helper.php. If you're using the default GD font go to line #193 and go ahead change the font size value. If you're using your own font change line #199.
The only trouble is when a newer version of CI comes out and upgrading your site's CI version will also mean changing those values again manually.
Ugly but works. I hope it helps.
