Face preservation refers to an AI image model's ability to keep a specific person's actual facial features, skin tone, and general likeness intact while changing everything else about the image.
Why this is the whole point
Without reliable face preservation, an 'AI transformation' app is really just generating a random person wearing the requested outfit — the actual value of a personalized photo app depends entirely on the output genuinely looking like the person who uploaded it.
What makes it technically hard
The model has to change pose, lighting, clothing, and background substantially while holding facial structure, proportions, and identifying features steady — a much harder task than either fully preserving the whole photo or fully regenerating it from scratch.
How to judge it in a result
A good face-preserved result should be immediately recognizable as the same person to anyone who knows them — if a result looks like a stranger who vaguely resembles the input photo, that's a sign of weaker face preservation.
Does a low-quality source photo hurt face preservation?
Yes — a clear, well-lit, forward-facing photo gives the model more reliable facial detail to preserve; a blurry, dark, or extreme-angle photo gives it less to work with, which can produce a less accurate likeness in the result.