With respect to Wikipedia, it can be edited by anyone so one can add proper attribution without any problem. Because of serial number, a currency note is easy, if one still owns it. After it is sold shouldn't it pass to the new owner? Common coins are more difficult, but I once claimed copyright to Wikipedia and it was granted, since reflection off the coin surface in scan, showed it was my image.

I have been uploading images to my website coins.lakdiva.org since 1998, and I have found those images used to sell coins on eBay, illustrate book covers, and even in publication of the Central Bank of Sri Lanka, without any attribution. Once when a local newspaper published over 100 of my images without any attribution I claimed and they paid me about US$150 without any fuss. If they had asked I would have allowed free use.

I recently found a large online collector website to which someone had uploaded large number of my images. To add insult to injury they had rewarded that member with a star recognition for his contribution of Sri Lankan coin images! When I complained they sent back a lot of legal paper work which they rightly predicted I will not have the motivation to waste my time on.

To fight back I am almost inclined to make an online web page on the plagiarism and provide the citations. In a way it is recognition that the information I put online is useful even though, citation by the user would have been better. Google image search does allow you to locate usage of your images online.