It Cannot Be the Photo You Already Have
Renewal closes the obvious shortcut.
The ICP states that the photograph must be recent, must comply with ICAO specifications, and must not be identical to the current photograph printed on the passport. The same sentence appears for the Emirates ID, with the ID substituted for the passport.
That last clause is the one that catches people. Renewing a passport is exactly the moment you reach for the photo you already own — it is the right size, it is already approved, and it is in your hand. It is also specifically excluded.
This is the same rule the UK applies to its ETA, where the guidance says the image must not be from a previously taken digital facial image. Two authorities, different documents, the same closing of the same loophole: a photograph proves what you look like now, and a copy of an old one proves only what you looked like then.
So take a new one, even if the old one still looks like you.