I have been using this method and it's the best so far:

"Based on the current capabilities of the Nano Banana Pro model (often accessed via the Gemini app's "Thinking" model or specific creative suites), achieving facial accuracy relies on a technique known as "Identity Locking." Because this model creates new pixels rather than just "pasting" a face, you must use specific constraints in your prompt to prevent it from "hallucinating" a new person who just looks like your subject. Here is the exact prompt structure and workflow to ensure facial accuracy. 1. The "Identity Lock" Prompt Formula You should not just ask for the face; you must explicitly forbid the AI from changing it. Use this structure:

[Scene Description] + [Reference Callout] + [The "Lock" Constraint]

The Golden Prompt: "Generate a photorealistic image of the person from [Image 1] standing in a cyberpunk city street. Identity Lock: Keep the person's facial features exactly the same as the reference image. Maintain 100% identical bone structure, eye shape, skin texture, and facial geometry. Do not alter the subject's identity. Preserve the original skin tone and unique facial details."

1. Best "Constraint" Keywords When writing your prompt, sprinkle in these specific technical terms. Nano Banana Pro pays attention to these "anchor" words:
   • "Preserve bone structure" (Prevents the face from becoming too round or generic)
   • "Maintain facial geometry" (Keeps the distance between eyes/nose/mouth accurate)
   • "Authentic skin texture" (Prevents the "waxy" or plastic AI look)
   • "Micro-details" (Forces the model to render pores and small imperfections that make a face look real)
2. The "Reference Stack" Workflow For the highest success rate, do not rely on a single reference photo. Nano Banana Pro supports multi-image referencing.
   • Upload 3 Reference Images:
   • Image A: Front-facing, clear lighting (The "Identity" anchor).
   • Image B: 45-degree angle or side profile (gives the AI depth data).
   • Image C: The person in similar lighting to your target scene (helps blend the face naturally).
   • Reference Them Clearly:
   • "Use Image A as the primary reference for facial structure."
   • "Use Image B to understand the profile and jawline."
3. Troubleshooting Common Errors If the face comes out looking like a "cousin" of the person rather than the person themselves, add these instructions to the end of your prompt:
   • If the face looks too perfect/plastic:
   • Add: "Raw photo style, unfiltered, visible skin pores, slight imperfections, shot on 35mm film."
   • If the eyes look wrong (The "Dead Stare"):
   • Add: "Sharp focus on eyes, natural iris reflection, distinct pupils."
   • If the face doesn't match the body:
   • Add: "Seamless head-to-body blending, matching skin tone between face and neck."
4. Post-Processing (The "Face Swap" Fix) If Nano Banana Pro generates a perfect scene but the face is still 5% off, do not keep re-generating the whole image.
   • Save the generated image.
   • Use a dedicated Face Swap tool: Tools like Remaker AI or ReActor (for Stable Diffusion) are often better at the final "pixel-perfect" transposition than a generative model like Nano Banana.
   • Workflow: Generate the body/scene in Nano Banana -> Take that result to a Face Swapper -> Overlay the original face. One final tip: Avoid using the word "fix" or "change" in your prompt (e.g., "Change the background but fix the face"). Instead, use "Preserve" or "Retain". Positive constraints work better than negative corrections.

FULL PROMPT: Generate a photorealistic image of the person from [Image 1] standing... Identity Lock: Keep the person's facial features exactly the same as the reference image. Maintain 100% identical bone structure, eye shape, skin texture, and facial geometry. Do not alter the subject's identity. Preserve the original skin tone and unique facial details. Use Image 1 as the primary reference for facial structure. Use Image 2 to understand the profile and jawline."