A campaign fails the moment the product changes shade between two shots. Locking is how you stop that happening.
The problem
Generate the same jar six times and you get six slightly different jars. The cap warms half a stop under a warm key light. The glass loses its frost. The label shifts a millimetre and the brand mark thins. Individually every image is fine; side by side on a PDP they’re obviously not the same object.
The fix is to describe the product in a fixed block of text that never changes between renders, and to state materials and colors as hard facts rather than descriptions the model is free to interpret.
Copy this
The hex value matters more than the adjective. “Off-white” drifts; a number gives the model something to hold onto when the key light disagrees.
“And stays open” exists because of a specific, repeatable failure: feed a model shot a closed-bottle master and it will helpfully re-cap the open bottle. Guardrails have to be written as instructions, not hopes.
The final clause is the one people leave out. Stating that the scene may not modify the product is a different instruction from describing the product, and the model treats it as one.
What to watch for
- Metallics drifting warm under a warm key · the most common break.
- Frosted or matte surfaces slowly gaining gloss over successive renders.
- The label creeping off-center or changing weight; that’s label territory.
- Any change at all when you only meant to change the background · that means you fed the wrong reference. See master.
The drill
Write the product block for something on your desk. Then generate it four times in four different scenes (white sweep, marble, wet stone, linen) changing nothing but the scene text. Open the four at full size and compare the product only, ignoring everything around it. Every difference you find is a line missing from your block. Add it and run again.
