Using coins for scale is discouraged as it 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 can also reinforce a geographical bias, and some coins' designs are copyrighted.
Ideally, a photograph should include a ruler with the subject (example) or an added scale marking.
SI ("metric") units are the most commonly used worldwide (see meter and centimeter).
Beryllium ore. Source: http://resourcescommittee.house.gov/subcommittees/emr/usgsweb/photogallery/ ; original upload in English Wikipedia, 3 August 2004 by Chris 73 [[en:Image:{{subst:PAGENAME}}]] {{PD-USGov-Interior-USGS-
इस फ़ाइल में बढ़ाई हुई जानकारी हैं, हो सकता है कि यह फ़ाइल बनाने में इस्तेमाल किये गए स्कैनर अथवा कैमेरा से यह प्राप्त हुई हैं। अगर यह फ़ाइल बदलदी गई है तो यह जानकारी नई फ़ाइल से मेल नहीं खाने की आशंका है।