Hard to say from the photo and its condition, but if it were dug in USA the odds are it is counterfeit, since my survey so far of ground found King George III coppers is showing so far 100% counterfeit for those that we can identify and if photos are not good by weight. Over 100 coppers in survey so far. Even in literature published about the percentage of counterfeits versus Regal the number are as high as 95%. Of course some British soldiers and other loyalists probably had a few regals that they brought over but for the most part even in England, counterfeits were widely distributed. It is the counterfeits that are the collectible coins by the way.
Weight is usually the biggest determining factor, but not always, due to wear sometimes, making it difficult to say by weight, but in general, I use the following for weight guidelines on KGIII coppers be Regal or Counterfeit.
A Regal was supposed to be between 141 to 166 grains or 9.2 grams to 10.8 grams
Most counterfeits I have weighed are 90 to 123 grains or approx 6 grams to 8 grams.
Most of the the colonial coin collector experts can tell rather quickly by the look of the coin, I do not have enough experience to say by look without comparing with photos of Regals, unless it is a rather crude counterfeit, which there are many of them.
The one in this post is not a crude example...
Here is a website that shows quite a few different counterfeits but it also has a good photo of what a Regal looks like for each year of King George III , 1770-1775.
http://www.geocities.com/copperclem/Counterfeits_page1.html
I highly recommend reading the section on the Notre Dame website about Counterfeits.
http://www.coins.nd.edu/ColCoin/ColCoinIntros/CtfBrit.intro.html
Don
