[j_not_j]

There are three more I have to use:

4x4 matrix: you are challenged with letter/number for row/column and must respond with the matrix entry. Not much better than totp; try to find it on your phone.

photo array: given an array of challenge photographs, select the one you know is your secret photo.

not-so-secret Q&A: what is your mother's maiden name? Name of your first car? Your second wife's third brother's cousin's name?

[mooreds]

Thanks for sharing these. Is the 4x4 matrix a shared secret you get at registration?

I've definitely seen photo array as an additional factor in a 3 factor setup, never as the second factor.