The audience already knows what you look like
Every other page on this site is about a photo that has to convince somebody. This one is not. The people who see your messenger picture are your family, your friends, the group chat from five-a-side, and the plumber. They know your face. Nothing about this photo has to establish competence, and a picture that tries to — jacket, studio backdrop, chin angled down — lands as faintly comic among people who saw you eating chips last week.
What it should do instead is be current and warm. The most common problem is not that the picture is unprofessional; it is that it is four years and one haircut out of date, or that it is a group photo cropped so tightly that half a stranger's shoulder is still in shot. Being recognisable to people who know you is a lower bar than looking impressive, but it is a bar a surprising number of profile pictures miss.
Nothing else you own renders this small
In a chat list your photo is a circle roughly the height of two lines of text, sitting next to a name and a message preview, on a phone screen held at arm's length. It is smaller than a professional network's thumbnail and much smaller than a meeting tile. That is the constraint the picture has to be built around, and it is the reason a photo that looks great in a gallery can be an unreadable grey oval in the list where it actually appears.
Everything follows from that. Crop closer than feels natural — the face should fill most of the circle, not sit politely in the middle of a wide shot. Wear one plain colour, because patterns turn into noise. Put something behind you that differs clearly in tone from your hair and skin. And check it on a phone, not a laptop, because the phone is the only screen it will ever be seen on.
Changing it is a small social event
Unlike a work directory, a messenger picture is seen by people who will notice it changed, and some of them will say so. That is not a reason to avoid changing it, but it is worth knowing that this photo carries a little signal the others do not — a new one after a haircut, a new job, or a hard year gets read as news, whether or not you meant it that way.
The practical upshot is to pick something you are happy to leave up for a couple of years rather than something that suits this month. A picture that is warm, close, well lit and undated by a season or a haircut you are about to grow out of will survive far longer than one taken at a specific event, which starts to look like a specific event the moment the event is over.
