But some of the purported benefits wobble upon closer inspection. Take the oft-repeated claim that satellite images are the sole source of "objective" information in bitter conflicts. That may be true relative to many other sources, but satellite images are only as valuable as the analysis of them is, and that analysis is subjective and occasionally subject to human error and confirmation bias. In the image above, it was analysts, not satellites, who visually contrasted healthy and unhealthy vegetation, and annotated the resulting picture to call viewers' attention to what they felt was significant. In 2013, after Human Rights Watch released a report on another massacre in Baga by the Nigerian military, the organization and Nigeria's National Space Research and Development Agency relied on satellite images to undercut each other's claims about what did or did not happen in the town. Satellites, too, can be spun differently by different sides in a conflict, particularly when the identity of the perpetrator of a given act of violence is in dispute.

The press, sometimes taking its cue from human-rights organizations and satellite companies, also tends to downplay the significant limitations of satellite imagery and to only highlight its successful deployment, rather than instances in which the technology proves inconclusive or contradicts reports of a human-rights abuse.

The satellite images of Baga, for instance, provided some of the first visual evidence of an attack whose existence up to that point was known primarily through fragments of witness testimony. They provided insights about the number of buildings destroyed and the population density of the towns, which could be combined to arrive at a very rough estimate of the death toll. But critically, the images captured burnt buildings, which—as with other dramatic changes to physical landscapes like the appearance of mass graves, the buildup of military hardware, or the deliberate demolition of homes—are relatively easy for satellites to spot. Instances of, say, small-arms fire by militias or violence carried out under dense cloud cover are essentially impossible to see from space. The satellites over Nigeria offered few clues about who carried out the attacks in Baga and Doro Gowon (in this case, witness testimony clearly pointed to Boko Haram), or where the killings occurred, or what sequence of events led to the deaths. Satellites, in other words, can only track certain kinds of violence, in certain ways.

For these reasons, satellite evidence is often at its best when paired with on-the-ground interviews and surveys. Witness testimony that Doro Gowon residents fled Boko Haram by boat across Lake Chad, for example, lent significance to Amnesty's observation that wooden fishing boats were visible by satellite along the town's shoreline on January 2 but gone by January 7. Researchers can make sense of satellite images by cross-referencing them with witness testimony, and the credibility of witness testimony can be bolstered or challenged with satellite images.

DigitalGlobe via Amnesty International

Andrew Herscher, an expert on the architecture of political violence at the University of Michigan, has identified other, less apparent downsides to the use of satellite imagery by human-rights groups. "Human rights satellite imaging takes place within a geography of closed territories and open skies—the geography of a world in which repressive regimes can prevent reporting of any human rights abuse and surveillance satellites can report freely on every such abuse," he wrote in a 2014 article for the journal Public Culture. This new geography is one "in which the satellite gaze makes a place for itself by negating the gaze of on-the-ground witnesses." Human-rights organizations, Herscher argues, are now using satellite imagery not just to corroborate eyewitness testimony but also to confirm it, and to substitute for and justify a lack of on-the-ground investigations in closed conflict zones like Boko Haram-held territory in Nigeria or ISIS-held territory in Syria and Iraq. In the case of the attack in Nigeria, the satellite images of Baga and Doro Gowon have now been widely distributed, even as both towns remain largely inaccessible to monitors on the ground.