I am now 98.52% certain that the click to open images was in fact a consequence of SpamSeive. The only instance since my first post was a SpamSeive false positive. All other incoming email works as divined.

Harv
27" i7 iMac (10.13.6), iPhone Xs Max (12.1)

Those who can make you believe absurdities can make you commit atrocities. ~Voltaire