What the achievement asks
Take 100 Great Shots while cataloguing wildlife. Ten points, account-wide.
Cataloguing world quests put you on a boat down a river or in a balloon over a zone, with a camera. A hundred good photographs sounds like a hundred rides. It is not, and the difference is one trick.
What counts as a great shot
Pointing the camera at an animal is not enough. Each group of wildlife performs a small action on a loop, and the photograph only counts when you catch it mid-action.
Eligible wildlife has a blue hue when your camera is pointed at it. That tint is the game telling you the shot will count. If there is no tint, waiting will not help: move the camera on.
Actions people have confirmed as counting include a beaver carrying a log, a goat jumping, and a salamander growling. The pattern is consistent: something is happening, rather than something standing still.
The trick that turns weeks into an evening
The cataloguing world quest does not complete while you are in a raid group. Convert your party to a raid, or join one, before you start, and you can ride the same tour over and over without the quest ever ticking off.
That removes the entire constraint. Instead of one ride per world quest and waiting days for the next rotation, you take a hundred photographs across as many consecutive rides as you feel like.
The same effect comes from abandoning the quest once your progress bar reaches full, which works if you would rather not bother with a raid group. Take the quest, ride, abandon at 100%, take it again.
The ride to spend your time on
The balloon ride over Thaldraszus is the one worth repeating. The marmoni along its route are almost always mid-gesture, waving their arms about, so nearly every pass produces shots where other routes produce a handful.
The Ohn'ahran Plains river tour is the other reliable one, and it has the advantage of being the same sequence of events every run, so after two or three rides you know exactly where to point the camera and when.
Where it fits
One of eight under Wake Me Up, which rewards a Bestowed Ohuna Spotter and is a piece of A World Awoken. Do it on the same rides as A Legendary Album, which wants seven specific characters photographed and uses exactly the same raid-group trick.