The plugin doesn't do cleaning temporary folder

same problem, and it will cause loading very slow, i just delete 10000+files. it is possible for the plugin delete it automatically?

I had the same problem. Got rid of it by modifying these lines in really-simple-captcha.php (permissions of the temporary files then become read AND write so they can be deleted by the plugin each one hour):

/* Mode of temporary image files */
$this->file_mode = 0444;

/* Mode of temporary answer text files */
$this->answer_file_mode = 0440;

to

/* Mode of temporary image files */
$this->file_mode = 0666;

/* Mode of temporary answer text files */
$this->answer_file_mode = 0666;

I found it works on my online server, but not working on XAMPP.

Have the same problem on localhost on WAMP 2.2
Rene Puchinger solution solve the problem (change 0444 and 0440 to 0666)