There's no such thing as free bitcoin.
You have to spend something* to get bitcoin.
*time: "solving captchas" on blockchain
*time & energy: "to join sig campaigns and post messages" etc.
Can you describe more about "solving captchas" on blockchain? I might be interested in it.
That is called going to faucets. Every faucet required you to solve a captcha and they will give you a few hundred satoshi. You can't get a lot doing that though.