[derefr]

That example is not about positive proof (i.e. proving that real evidence is real); it's about negative proof (i.e. proving that fake evidence is fake.) It's about having a way to figure out that the expert defending the evidence has been bribed, and is saying what the prosecution wants them to say.

You can't charge someone with perjury if you can't prove the faked evidence is faked—which is why so few people get charged with perjury. Any threat of perjury with no discriminatory proof mechanism to back it up, is toothless, and experts will treat such threats with exactly the respect they deserve. (Look at the Japanese court system if you don't believe me.)