Ah, what a pitty .. for the future I will post all keys only in picture-format. Seems better than any other option to keep ninja-bots away ;-)
Haha, I wonder if there are somewhere steam bots using advanced methods resolving the captchas... :)))
Personally I think the best way is to insert some kind of easy for human task to do with the key.
For example: ABCDEFGXIJKLMNO and then adding "replace X between G and I and insert - where needed".
I hope you don't feel offended by my little lecture. Giveaways are nice thing, but they need a minimum attention to be done properly - otherwise keys are simply wasted.