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صورة:PhosphateRockUSGOV.jpg


Phosphate rock

Source: http://resourcescommittee.house.gov/subcommittees/emr/usgsweb/photogallery/ ; English Wikipedia, original upload 3 August 2004 by Chris 73

Public domain This image is a work of the "Minerals in Your World" project, a cooperative effort between the United States Geological Survey and the Mineral Information Institute. The images were featured in the "Minerals and Materials Photo Gallery" on the website of the U.S House Subcommittee on Energy and Natural Resources. As a work of the U.S. federal government, the image is in the public domain.
U.S. quarter

This image has currency in it to indicate scale.

Avoid using objects such as coins for scale, as they will require people unfamiliar with them to look up the dimensions or guess, both of which defeat the purpose of the object in the first place. Coins are particularly bad as they can reinforce a geographical bias, and some coins' designs are not free content.

Ideally, a photograph should include a ruler with the subject (as seen in this photo) or add a scale marking via an image editor instead (as seen in this photo). SI/metric units are the most commonly used worldwide (see metre, 1 E-2 m).

Examples of bad practice: here.

A tape measure


Common coin diameters for reference:

  • U.S. dollar:
    • : 19 mm, 0.75 in
    • : 20 mm, 0.79 in
    • 10¢: 18 mm, 0.71 in
    • 25¢: 24 mm, 0.95 in
    • 50¢: 31 mm, 1.21 in
    • $1: 26 mm, 1.02 in
  • Canadian dollar:
    • : 19 mm, 0.75 in
    • : 21 mm, 0.83 in
    • 10¢: 18 mm, 0.71 in
    • 25¢: 24 mm, 0.94 in
    • 50¢: 27 mm, 1.07 in
    • $1: 26 mm, 1.04 in
    • $2: 28 mm, 1.10 in
  • Pound sterling
    • 1p: 20.32 mm, 0.80 in
    • 2p: 25.91 mm, 1.02 in
    • 5p: 18.00 mm, 0.71 in
    • 10p: 24.50 mm, 0.96 in
    • 20p: 21.40 mm, 0.84 in
    • 50p: 27.30 mm, 1.07 in
    • £1: 22.50 mm, 0.89 in
    • £2: 28.40 mm, 1.12 in
  • Euro
    • 1c: 16.25 mm, 0.64 in
    • 2c: 18.75 mm, 0.74 in
    • 5c: 21.25 mm, 0.84 in
    • 10c: 19.75 mm, 0.78 in
    • 20c: 22.25 mm, 0.88 in
    • 50c: 24.25 mm, 0.95 in
    • €1: 23.25 mm, 0.92 in
    • €2: 25.75 mm, 1.01 in

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