I've found these messages in my error logs, since I upgraded to 1.10.2:

[error] b2evolution error: Call to non-htsrv Plugin method! in /blog/anarco/call_plugin.php at line 72 / REQUEST_URI:  /blog/anarco/call_plugin.php?plugin_ID=17&method=display_captcha&params=a%3A1%3A%7Bs%3A6%3A%22pubkey%22%3Bs%3A32%3A%221f03480b50aace74526fb916e4c5be15%22%3B%7D / HTTP_REFERER: -

And I don't know if this is an error coming from the captcha_img_plugin, or is it due to the fact that I renamed the "htsrv" directory as "anarco". In any case, the captcha images are still displaying, as far as I know and no other inconvenience has appeared, so I don't know if I should call this a "bug" or just an annoyance, since it hasn't given me any trouble, really.