Photo shops charge for a handful of passport photos, and the job is really just printing the same small picture several times on one sheet at exactly the right scale.
The single most common mistake is letting the printer fit the image to the page. Fit to page nudges everything by a few per cent, which is invisible to the eye and fatal for a document where the size is measured. Turn scaling off, choose actual size, and the millimetres come out right.
The second is paper. Ordinary office paper absorbs ink and the result looks washed out and feels wrong to anyone handling it. Photo paper costs little and is what the counter uses.
If you are printing at a shop, hand over the sheet rather than the single photo. A shop asked for one small picture will often scale it to fill the paper, which puts you back where you started.
It depends on the size your country requires. The sheet is filled automatically and the count is shown before you save.
Cutting guides. They mark the exact edge so you can trim accurately with scissors or a trimmer.
Yes, that option is there too, though 4 by 6 photo paper is cheaper at a print counter and wastes less.