The image comes from a Reddit post, with this explanation:
Was walking on the local trail today, going through the forest part. When suddenly I feel a very sharp pain in my arm, like a shot. Look down and there is a long dart, from maybe a blow gun of sorts? I don't know but scared the shit out of me, I looked and could see no one.A simple Google Image search yields a wide array of photos of this weaponry. The Reddit thread focuses on potential health consequences (probably minimal other than at the site of entry) and the range (up to about 100 feet, if you want to locate and try to wreak retribution on the malefactor).