These are large silver Japanese coins from the late 1800s and early 1900s. Some of these coins are quite valuable, cataloging for thousands of US dollars in uncirculated condition, and falling as low as $50 or so in worn condition. The coin in the picture is probably not fully uncirculated, but it is very close.
Proper evaluation of these coins requires a detailed knowledge of the Japanese characters. For typical Westerners (like me!), the first order of business is to determine the date on the coin. A good place to do this is at AllCalendars.net.
Glo's coin in the picture is dated 1874, the 7th year of the Meiji dynasty, Emperor Mutsuhito, and it is a valuable coin. Genuine coins contain 0.78 troy ounces of silver. Here are typical catalog values for most dates of these coins:
worn: $30 US dollars approximate catalog value
average circulated: $55
well preserved: $100
fully uncirculated: $350
As always at CoinQuest, these are catalog values and subject to the diminishing effects explained on our Terminology page.
The catalogs list the following dates as more valuable than the common dated above. The values after each date are catalog values for average circulated coins:
Dating the coin, however, is only half the battle. What remains is authentication and grading. Authentication means determining whether or not the coin in genuine. Grading means determining the amount of wear the coin has received. In Glo's case, authentication is much more important than grading. It is clear that the coin has not received much wear, but it is not clear that the coin is genuine.
Another coin like this [PRESS HERE] proved to be a counterfeit. Be sure to look at it because there is a side-by-side comparison of real and fake coins. Glo's yen, shown in the picture on this page, appears to be counterfeit.
The picture shows a Japanese yen authenticated and graded by NGC, a major third party numismatic grading service. This coin is authentic. If it were not, NGC would not have installed it in the plastic holder bearing their name.
Counterfeiting rare collectible coins has always been a problem, but in recent years a cadre of counterfeiting shops have grown up and started mass producing fake rare coins on large scales. These are located mostly in China, but China is not the only place producing counterfeit rare coins. If you are a well-financed crook and want high quality counterfeits, you can find people who will make them for you. Glo's yen coin is valuable, and that alone qualifies it for being a counterfeit.
Many times detecting counterfeit coins is easy. The fakes look different than the real coins to anyone who has collected for a few years. But sometimes it takes microscopic examination to sort the tares from the wheat.
One of the biggest factors in determining authenticity is the history of the coin. If a coin has been in the family for decades, it is not a modern Chinese fake. If you bought it on eBay last week, there is a strong possibility that it is a fake.
My recommendation for Glo is that she have the coin authenticated and graded by one of the following services: PCGS, NGC, ICG, or ANACS. They are all easy to find on the web and they are the only services universally recognized as trustworthy by the numismatic community.