After logging in, I do can report a bug (I have to fill in a captcha but it works).
When I was not logged in, I either got the reject message without a captcha or I got a captcha that wouldn't work (i.e. after typing in the captcha words, it would be rejected anyway).
My point is: if a bug report by a non-logged-in user is going to be rejected ANYWAY, then don't give the opportunity to write it (not for the sake of fighting spam, for the sake of not make users waste time).
Or if non-logged-in submission IS supposed to work with the captcha, then be informed that it doesn't. Maybe the captcha is simply broken. (yes I tried it multiple times, I may have misspelled once, but not five times).