NASA's Perseverance Mars Rover

These are Fiducial Markers (or fiducials for short). Fiducials basically allow the rover's computers to measure itself.

The markings are a staple of engineering that can serve two parallel purposes, to calibrate cameras and to calibrate various mechanisms on the rover.

They’re a common feature in high-tech photography and robotics here on Earth, but the use of fiducials on extra-terrestrial robots is relatively new.

The technique started informally on the Mars Exploration Rover (MER) mission, which landed Spirit and Opportunity on the Red Planet’s surface in 2004.

JPL engineers noticed that, over time, the accuracy of the MER robotic arm was degrading, and they weren’t really sure why. So some of the JPL engineers came up with an algorithm that would just recognize a circular feature on the end of the arm. Then every day, it could track where that actually was versus where the robotic rovers thought it was. The idea blossomed into more than just an engineering hack with Curiosity. JPL engineers came up with the design for the fiducials for Curiosity, as they needed something that would be easy for either a computer program or a person to accurately pick the center of. Having that intersection in the middle makes it easier for a person, as they can zoom in on the image and click exactly on that intersection, and the design also makes it easy for a computer, because it can compute the center of a circle. From there, basic trigonometry lets engineers piece together the positions and orientations of the various parts of the rover.

To measure all of the mechanisms on the rover, fiducials are installed all over the turret, on the end of the rover's arm, as well as on the tops of the steering actuators and on the top deck of the rover.

They were so useful they are were installed on the Mars Insight lander and the M2020 rover.

M2020 also uses the smaller 'April Tags'. They're fiducial markers for machine vision systems and are "robust to lighting and viewing angle".

These are aruco indices. Each represent a unique index. They are popularly used in robotics for all sorts of things. I'd imagine they serve some kind of recalibration purposes for this camera.

Since they know the exact position and rotation of the camera in relation to these markers, they can check if the markers move by small amounts, which would mean lens distortion.

I could be wrong though, since you would typically need quite a lot of them at different depths for a full camera calibration.

Actually maybe they're used to measure vibrations in the drill? The vibration data would be a lot smaller to download than a full video file, so they might process that info on site and send it back

It's for martians, so they know in which bin to recycle

I think so. I know at the robotics lab in my uni they had lots of those mini qr codes on the walls.

Iirc there was something about a self steering trailer that looked at a grid of four of those codes on the leading vehicle.