I think I have an interesting idea for a captcha.
How about letting anons contribute questions in only Indian scripts and languages which may be used as the captcha (allowing the user to select their desired language to get the question in). These may be one word answer questions, allowing the answers to be written in English for the convenience of the user.
"ठंडा का विलोम शबद कया है?"
("what is the opposite of cold?")
Answers may be:
'warm', 'hot', 'गरम' and so on for other languages.
Rasterisation/imagification of the hindi/ regional language scripts via Imagemagick shouldn't be very hard.
This may hinder foreign users from posting but it will allow Indian VPN users to post.