They can be tricky, and it's most annoying when despite your best efforts at deciphering it, it still says you got it wrong. We're looking at ways to improve this feature, what we're likely to do is turn off the requirement to verify the image if you're a member with more than X posts. This way trusted folk are not inconvenienced, but the auto-bot spammers still get caught out.
They still suck as far as I'm concerned.
Also, have you fixed the problem where you have to verify the image at the preview stage (if you preview it), as well as the actual sending stage?
You said you were going to fix this, I seem to remember.
Also: When are you going to start allowing attachments in PMs?
PMs are a form of email (a pretty clunky one, but still a form of email) and email has had attachments just about forever. Seems a woeful lack.
"But why would you want to send an attachment in a PM Mike?"
Well, for example to send a chart to a mate, with suggestions about a trade, or questions thereof, etc.
I suppose you couldn't stop people just using it to send dirty pictures, but, well, you're always going to get twits, whatever you do. I dare say a few spot-checks would eventually catch them out.
You would have to do some virus checking, but I imagine you have to do this already for attachments to postings, so can't be too much extra work.