Hi!
I had this issue with a few surveys of others already (I am not using captchas nor am I planning to).
However, whenever I go for a survey that requires captchas I can't access them.
Either I am really, really bad a simple maths, or there is something wrong when using the surveys with Google Chrome.
Here an example:
web-meinung.de/limes/index.php?sid=13545...mal&loadsecurity=102
Tested it with Chrome = doesn't let me in, even after several attempts.
With Firefox I managed to get past the capture on the first attempt.
As I said, this happend to me before with Limesurvey, but also with other captchas as far as I recall.