Pibble is a Blockchain based image Cryptocurrency. It is a monetized Image Ecosystem that brings image creators and consumers together and aims to reward image makers.
For more info about the Airdrop, visit Pibble Medium blog. Here you will see that currently there are 4 events ongoing.
Note that only event 2 is a free airdrop. Events 1, 3, 4 require some sort of payment.