[mplanchard]

Assuming the police didn't lie about the connection and the warrant was issued by a judge, both of those things would be fine. The issue in this case is that the police were not forthcoming about the source of the connection, and the connection itself was from a tool that explicitly says that it is not admissible in court. The warrant was obtained based on false pretenses, making the subsequent search illegal.

A judge probably would not rule in favor of a warrant based solely on a tool whose utility is entirely unproven and which itself warns that it should not be relied upon as evidence, while they might rule in favor of eyewitness testimony.

[Edman274]

But a random passerby also isn't admissible in court but could be used as a tip, right? If an anonymous person calls the cops and says "I heard someone say that Bob did it", there's no chance in hell that an anonymous person's hearsay could be admitted as evidence in any court, but if the cops get that tip, decide to check Bob's social media and decide that Bob looks a lot like the guy in their CCTV footage, they're not getting a warrant for a search based solely on the inadmissible hearsay, they're getting it based on their determination that the tip that they got does happen to match the footage they have. If they had to manually make a determination about whether a given person's face matched up with their CCTV footage and the warrant was issued on their determination that it does, it seems very complicated to then figure out to what extent the tip itself has to be admissible as evidence, right? Like, if a psychic called a police department with a tip and the cops put a house under surveillance and the surveillance reveals probable cause to get a warrant, should that kill the case because the tip came from supernatural sources?

[mplanchard]

Again, if the police have sufficient evidence to convince a judge that a warrant is justified, it doesn't really matter what the evidence is, only that it is not misrepresented to the judge and that the judge deems it sufficient.

The main problem in this case was the fact that the police misrepresented their evidence to the judge. It is theoretically possible that a judge may have issued a warrant on the basis of the facial recognition tool, in which case the evidence from the search would not necessarily need to be thrown out. If that were the case, I'd expect the defense to appeal the validity of the warrant, in which case all the questions you're asking would come into play.