Interior decorators, and even homeowners, display photos on a staircase based on personal preference. Photos, clustered by subject, could provide a snapshot of family life. Random placement invites scrutiny when people are walking up or down the stairs. A series of photos arranged from oldest to newest gives viewers a sense of continuity or a glimpse of history. For a clean, elegant look, arrange the photos in a line that mimic the rise of the stairs.
Stand on the lowest step and face the wall. Look up about 6 inches and make a small pencil mark on the spot you're looking at. Measure the distance from the stair to the mark on the wall.
Face the wall while standing on the highest step but not the landing. Mark a spot at the same height as the measurement you made on the bottom step.
Attach one end of twine to the wall with a tack or pushpin at the pencil mark. Do the same at the other end, making a straight line of twine from the top stair to the bottom stair about 6 inches above eye-level.
Arrange photos on the floor in the order you want to hang them. Hanging them in order of size, with the largest photo at the bottom of the staircase and the smallest at the top, will create an optical illusion that makes the stairwell seem higher. Use a tape measure to help space the photos at equal distances.
Install a picture hanger next to the tack at the bottom of the string line and hang the largest picture. Do the same with the smallest picture at the top of the stairs. Attach picture hangers to the wall along the twine at distances measured between the photos, plus one half the width of a picture. This will centre the photograph. You might have to make small adjustments as you go along depending on the number of photos and their sizes.
Remove the twine and hang the rest of the photos.
If you decide to use a chalk line rather than twine, select a colour that closely matches the wall colour. Chalk can be difficult to remove from painted surfaces.