Why passive income? When you participate in bounty campaign, you make the day-to-day work. I think passive income is more like money received regularly without effort.
Passive income is investing money and watching how your investments grow, but you still need to monitor news and etc. Bounty is like a real job when you need to be active every day and have good discipline
First i want to say that joining a bounty is not passive income since we need to do a job or task to get a reward. Anyway, before I join the bounty campaign or signature campaign I just check the ICO first if it is legit, I check their team, watching the video of their project, read their whitepaper, if it seems promising then you should join that bounty. So we can get our reward based on our prederence.