The photograph in the slideshow.

01 · The screenThe aspect ratio problem, and what to do about it.

Nearly every screen a slideshow plays on is 16:9 landscape: a projector, a large television, a laptop mirrored to a screen. Most family photographs of the last forty years are landscape 3:2 and fit reasonably. Most formal portraits, and almost all older photographs, are portrait — and that is where the trouble starts.

There are three ways to handle a portrait photograph on a landscape screen, and one of them is clearly best:

1. Blurred fill — the photograph sits whole in the centre with a blurred, enlarged copy of itself filling the sides. This is what most slideshow apps and presentation tools do automatically, and it looks considerably better than people expect. It is the right default.
2. Black bars — honest, quiet, and completely acceptable on a large screen in a chapel. Nobody has ever left a funeral because of letterboxing.
3. Cropping to fill — fills the screen and is the one to avoid. It removes the top and bottom of the frame, which on a portrait photograph means the hair, the chin, or both.

If your tool defaults to cropping-to-fill, change it. This single setting causes most of the "why does Dad look odd in the slideshow" moments.

02 · Resolution1920 × 1080 is a low bar, which is a mercy.

The screen is the least demanding output of the week. A 1920 × 1080 frame is 2 megapixels, so a messaging-app copy at 1600 pixels wide is genuinely adequate, and a scanned 4 × 6 is generous.

What to avoid is the reverse: a modern 48-megapixel phone photograph dropped into a slideshow at full size. Some tools will stutter on large files, and a few will fail to load them at all on an older laptop at the venue. Export the slideshow as a video file once it is built, rather than playing the source photographs live, and the playback becomes a single file that either plays or does not.

03 · The editHow many photographs, and in what order.

Length. Three to five minutes. Beyond six minutes the room has stopped watching and started waiting, and the music has usually finished being incidental. Forty to sixty photographs at about five seconds each is the shape of a well-judged one.

Order. Chronological is the default and it is hard to beat, because it carries the room through a life without anyone having to be told what they are looking at. Two variations that work: start with the most recent photograph and go backwards, which is gentler for some families; or use three chapters with a single photograph held longer between them.

What to include. The person's whole life, not only their best photographs. A blurred holiday snap from 1987 with their whole family in it does more than another studio portrait. Include the photographs that make people laugh — a terrible haircut, a ridiculous hat, a baby in a basin. The service already has the grief covered; the slideshow is allowed to be warm.

What to leave out. Anything that only the immediate family will understand, photographs of people the room will not recognise at the centre of the frame, and images with a heavy filter or an overlay that has aged badly.

04 · Sound and paceThe music, and the five-second rule.

One piece of music, two at most. It should be quiet enough to talk over, because people will talk — this usually plays before a service starts, in a room that is filling up, not during a moment of silence.

Five seconds per photograph is longer than it feels when you are building it and shorter than it feels when you are watching. If you are unsure, watch the whole thing once, start to finish, without touching anything. Everyone who builds one of these skips this step and everyone who skips it wishes they had not, usually because one photograph turns out to be a duplicate, or upside down, or of the wrong person.

Set it to loop if it will run before the service begins. Fifteen minutes of a slideshow that ends and sits on a black screen while people arrive is worse than one that quietly repeats.