Who do you think is I/me/you in the picture?
Solution 1:
All your 6 examples are grammatical.
I would read #1 as meaning something like "of all the people in the picture, which one is me? can you guess?".
I feel #4 has a broader range of possible interpretations. #4 could mean something like "Who do you think I am (pretending to be)?" or "Who do you think I am (representing)?"