With Pokemon GO-ing viral, it only makes sense to write a question about the iconic game. Let's say that somehow, scientists decided that the Professor Oak style of research (giving a kid a pokedex and telling them to "Catch them all") was the way to go, they choose little 10 year old Billy, give him the new biodex and tell him to take a photo of all animal species on Earth. Does little Billy have a hope of ever completing the Biodex? If he does, how many years will it take him?
I don't think it's possible to operationalise an answer to this, but one thing that leaps out at me is that certain "legendary species" might take years to find just in themselves — I can't find any sources to support this right now, but anecdotally I feel like I've heard of people spending months or years just trying to catch a glimpse of particularly elusive animals with very low populations in difficult habitats, like snow leopards, or tiny marsupial mice, et cetera. There's also the question of what goes on the list; this is maybe a nitpick, but does Billy have to "catch" every animal which is currently not extinct, whether we know for sure or not? One example from Australia is the thylacine or Tasmanian tiger; the scientific consensus is that the last one died in captivity in 1936, and no sightings have been confirmed for 50 years, which is apparently the official criterion for extinction. Nevertheless, if the species has survived, unbeknownst to biologists (but apparently "beknownst" by the "Centre for Fortean Zoology"), does Billy have to find one to complete his biodex? There are a number of "unconfirmable" extinction cases of this kind, I would imagine, even moreso in the sea. Gray whales are quite probably extinct, but the ocean is a pretty big place — and the absence of evidence is not technically the evidence of absence, as they say.
I feel like the closest analogue to what Billy needs to do is the career of David Attenborough, who has personally photographed an enormous variety of animals all over the world — I wonder what percentage of the world's total species count he has covered in his lifetime?
Surely (making it sound like it's nothing) with all the databases in existence one would not need to go catch them all, just link various identification criteria to each species to give an accurate enough id and the monotony of data entry, just like to point out obviously I know nothing about developing such a monstrous tool I was just curious if it is even possible to create a compendium of all living organisms.