Obviously, Starlink satellites are equipped with sensors for attitude and location detection (like a star tracker or sun tracker) but I'm wondering if they have with any direct Earth observation equipment, specifically cameras (even with only a low spacial resolution).
As of October 2022 it appears that yes there can be cameras that produce still and video images for downlink.
As reported by CNET here on 7th October 2022 Elon Musk tweeted a still image and a video clip of a re-entry burn as seen from a Starlink satellite. The camera appears positioned to observe the solar panel operation and as such has a very wide, almost 180 degree field of view, and once unfolded it would appear the panel will occupy much of that. It is unclear if all satellites have this camera fitted or just some. The fact that the tweeted images include a chain of satellites may mean a small number of camera equipped satellites monitor the overall flock deployment.
The best that this sort of camera could do would be km resolution, possibly useful for weather or environmental monitoring purposes but would need a very different lens assembly to make a 'spy sat', at least akin to a telephoto lens on a consumer DLSR which would be complex to fit into the notably thin Starlink chassis.
It is worth noting that there are already constellations of small imaging satellites like Dove which would make adding several kg of long lens optics to a communications constellation a questionable business decision.
Yes, they do. Spaceflight Now reports, via a 2019 May 15 press kit from SpaceX, that
The satellites also host optical trackers to detect space debris, allowing the craft to autonomously avoid collisions with other objects in space.
Such a tracker would see the Earth much of the time, being in such a low orbit.
SpaceX's press release dated "May 2019" says that
each spacecraft is equipped with a Startracker navigation system that allows SpaceX to point the satellites with precision. Importantly, Starlink satellites are capable of tracking on-orbit debris and autonomously avoiding collision.
The cameras might not be part of the "Startracker navigation system" per se. NASA says, without mentioning any onboard sensors, that
The Startracker navigation system is based on the heritage of Dragon. The satellites are designed [to] autonomously avoid collisions based on uplinked tracking data.
Yes, they do, at least in the form of star tracker cameras that have sometimes pointed at the Earth. On 2020 April 28, SpaceX reported that
We're currently testing rolling the satellite so the vector of the Sun is in-plane with the satellite body, i.e. so the satellite is knife-edge to the Sun. ... The star tracker cameras are located on the sides of the chassis. Rolling knife edge to the Sun can point one star tracker directly at the Earth and the other one directly at the Sun...