All too often images of coins are posted to Wikimedia and elsewhere which are of less than stellar quality. In one case the images highlighting an article's subect were so poor that you couldn't even tell what kind of coin it was! This is usually because a regular digital camera is used to take the picture. Though digital and film cameras can take excellent coin pictures with the right equipment and technique, the typical wiki user and ebay seller has neither.
Fortunately there is a very easy solution to this problem, that is to scan the coin directly using an ordinary flatbed scanner. Such scanners can often be purchased for less than $100, sometimes less than $50. Even deluxe models are usually less than $200, but coin scanning doesn't require an expensive transparency adaptor.
The technique really is as simple as just placing the coin on the scanner bed and scanning it, and the results are vastly superior to what could be done with an ordinary digital or film camera, see examples below.
Coins are not the only objects that can imaged this way, many small objects on eBay might fetch higher bids if they were illustrated with scanner pics instead of the dark, blurry images many sellers produce with digital cameras.
In most cases you will want turn the brightness all the way up when scanning since coins tend to come out dark.You also should also remove dust and debris from both the scanner and the coin as small particles show up prominently in high resolution scans.
Be careful of how the coin is oriented. Putting it on the bed proerly aligned is more difficult than it would seem, though this can to some extent be corrected with software.
Though bright shiny coins look impressive in your collection, they aren't always the best subjects for imaging. Duller coins that still have all their details will often produce better images.
I typically scan at 2400 dpi but 1200 is enough for most purposes. In my experience large images reduced in size look better than small images originally scanned at a low resolution.
Instead of doing a "prescan" of each coin you might find it easier to scan a large area and then use cropping to adjust the image afterward.