I found it interesting that you found so much information on the once "mysterious" Vassili Yakovlev plus a photograph. According to your footnotes, the person who was your main source was Yaklov Yurovsky.
Sorry, but you're wrong here. The main source for Myachin-Yakovlev's story was Myachin-Yakovlev himself. There are unpublished memoirs written by him at two archives: TsDOOSO, fond 221 op. 2 d. 964 and the Party Archives of Bashkirov, fond 1832. We quote from both of them, and both of them are correctly sourced in our notes. We also quote and source several published works, for example, Mstislavsky and Kobylinsky via Sokolov. Yakov Yurovsky is NOT our "main source" for information on Myachin-Yakovlev.
Where was the photograph found?
AGRBear
We purchased our photo of Myachin-Yakovlev from a private collector with impeccable sources. There is another version of our photo which appears in Love, Power and Tragedy, though theirs bears official stamps and seals, and ours does not. It is undoubtedly the same man, if you want to check.
Penny