What the specification means in practice
Nothing else on this list is 33 × 48 mm, so a Chinese visa photo cannot be cut down from a 35 × 45 mm European photo or a 51 × 51 mm American one without falling outside the head-size rules. The specification is also unusual in constraining two dimensions of the head: 28 to 33 mm in height and 15 to 22 mm in width. Head width is effectively a rule about how far you are from the camera and how much the lens is distorting your face.
Why the width constraint matters
Head height alone does not tell you whether a face is being reproduced faithfully. A photo taken very close to the lens produces a face that is tall enough but disproportionately wide through the cheeks, with the ears compressed. The 15–22 mm width band catches that.
The practical consequence is the same advice as everywhere else, but with a specific reason behind it: shoot from about a metre and a half away and crop, rather than filling the frame at arm’s length.
Head position is specified in degrees
The tolerance is explicit: no more than 20 degrees of left or right tilt, and no more than 25 degrees of up or down tilt. That is unusually precise for a photo standard, and it is a useful check — if you can see more of one ear than the other, or the underside of your chin, you are outside it.
Your ears must be visible, which is a requirement several other countries do not make. Long hair tucked behind the ears rather than falling in front of them makes this straightforward.
Glasses are allowed, with conditions
Eyeglasses are permitted except thick-rimmed, tinted or glare glasses. In other words: the frames must not obscure the shape of the eye sockets, the lenses must be clear, and there must be no reflection sitting over the eye. If your everyday frames are heavy, borrow lighter ones or take the photo without.
Background and expression
The background must be white or close to white, with no edge frame around the printed photo. A photo taken in an everyday setting — at home, outdoors, at a desk — is explicitly not accepted, even if the background behind you happens to be pale.
The expression must be neutral with eyes open and lips closed. Facial features must be complete and clearly visible, with the head centred in the photo. The photo must be in natural tone: not over- or under-exposed, no red eye, no distortion.
Recency and headwear
The photo must be taken within the last six months, in colour, bare-headed and full face. Hats and other head wear are permitted only for religious reasons, and even then must not obscure any facial feature.
Requirements are published by the Chinese Visa Application Service Centres, and the centre handling your application is the one to check against — service centres in different countries occasionally add local submission details on top of the common photo standard.