1 · Hide one model draws the picture
The model is told to draw the scene you name and to bury your secret in how it draws it — the count of things, their order, spacing, a tint, negative space. It may not write the secret as text.
2 · Look a different model, fresh context
Only the rendered picture is shown, in a new request with no memory of the secret. It answers whether anything is hidden and what it reads.
How it was hidden (spoiler)
Encoding:
Hint for a human: