Could you give me some pointers/hints (or even specific examples) where I'd find this in use? I ask because IIRC I've never seen ReCaptcha be used on file host

Could you give me some pointers/hints (or even specific examples) where I'd find this in use? I ask because IIRC I've never seen ReCaptcha be used on file hosting sites. (I don't think so, at least. There might be one...)