How many photos do you need for a photo mosaic?

Every mosaic here is a grid of 40 tiles across and 50 down, which is 2,000 tiles. A page accepts up to 500 photos.

When there are fewer photos than tiles, photos repeat to fill the grid. With 100 photos, each one appears about 20 times. With 500, each appears about 4 times. Everyone who adds a photo appears at least once, and a new photo always takes the place of a repeat rather than pushing someone out.

Each tile is lightly tinted toward the colour that part of the picture needs. That tint is what makes the picture readable from a distance, so the mosaic looks like your picture from the very first upload.

What more photos add is variety. With 10 photos you will see the same faces in rows. Somewhere around 50 to 100 the repeats stop being obvious at a glance. Past 200, most people need to zoom in to find a repeat at all.

Each photo is placed in the free tile whose colour is closest to the photo's own average colour. A set of photos that are all dark, such as indoor party pictures, gives the layout little to work with in the bright areas. Outdoor photos, pale backgrounds and a few close-ups against the sky fill the light parts well.

You do not need to manage this. Just ask a wide group of people, and the variety arrives on its own.

The print-ready download is 9600 by 12000 pixels, with each tile 240 pixels square. Printed at 300 pixels per inch that is 32 by 40 inches, with each tile 0.8 inches wide. Faces are easy to make out at that size.

The number of photos does not change the file size. A print made with 60 photos is exactly as sharp as one made with 500; it simply repeats more.