The question is vague but here goes. A trained eye will always be able to easily spot original work from a copy.
If you're speaking about content however, you're pretty much out of luck unless you have documentation of some sort.
If you're speaking about art you own which was made by another artist, there are professionals with tons of knowledge on the subject which you'd be hard press to research on your own.
This site may be able to help you, excerpt from site: About Alan Klevit
Expertise
I can provide sound advice on buying, collecting & understanding fine art, especially original works by 20th century masters and leading contemporary artists. I can also explain techniques used to create original works and offer tips on how to tell whether or not a piece is an original work of art. * http://en.allexperts.com/q/Fine-Art-3122/tell-painting-bought-real.htm
buzzkk@gmail.com
I have in my posetion a painting by keynaldo itis a painting of a spanish soldier can someone please tell me what its worth
This painting is at the Metropolitan Museum of Art. As far as I can tell, they own White Canadian Barn II.
original painting size 120 x 180 = € 24000 in 2011
I just got a Paul N. Norton watercolor painting Misty Morn at Mystic. I do not know if this is the original painting. Can somebody help me to determine if this is the original copy?
buzzkk@gmail.com
I have in my posetion a painting by keynaldo itis a painting of a spanish soldier can someone please tell me what its worth
I have it, but I don't know if it is an original? How do i tell? you can email me justmeizzy@hotmail.com
Yes
This painting is at the Metropolitan Museum of Art. As far as I can tell, they own White Canadian Barn II.
If you are talking about the original, nobody can tell what it is worth until it is up for sale. Reproductions are cheap.
I have the original painting. Im trying to find out who will buy it from me
There's no foolproof way to get an original painting; just buy a painting and hope it's not fake.
i have the painting framed and signed and think it maybe the original
yes, an original painting is more valuable than a print.
I have the original painting. Im trying to find out who will buy it from me
Sometimes there will be two original paintings. I've gotten it before. Just be careful, sometimes when you think the painting is original, it can be a forgery. Both Tom Nook (if you try to sell it, he won't buy it or give you only 10 Bells) and Blathers (will tell you it's a forgery when you try to donate it) can tell you if it's forged. If Blathers tells you, the name will be "forged painting" after you try to donate it.