how to tell whether a painting is an original or a print/reproduction?

Answer 1

There are several ways to go about identifying whether a piece of art in an original painting or whether is a copy or reproduction of a famous original, or just a nice painted work. If the work is signed, Google the name, and if you start seeing works popping up at the Museum of Modern Art or the Louvre, then it probably shouldn't be too hard to identify the piece you have in your hand, it's most likely either a nice production or a photograph. If you just want to tell the medium used in the piece here are several ways to identify different materials:
A print (etching, woodcut, linocut, etc.) may have indentations from the plate at the edges. A print that was struck in the proper manner should have an edition number (i.e.: 25/100), and often prints made of masterworks will have a stamp or embossment on the back of the print saying that the copy is an authorized copy.
Oil paint is generally thicker and generally done on canvas or canvas board. A typical sign of age with oil paint is cracking or crazing across the surface. Acrylic can be applied to both canvas and paper, and water color is generally done on paper.
A reproduction of a painting will generally be done in a nice multicolor bookplate, and you will be able to tell that it is not a painting by the even, consistent, usually glossy surface of the piece.
If you have any real questions about the authenticity of a painting or print, and you believe it may have some value, you can always send a photo of the piece to an evaluator at an auction house like Sotheby's, and they will usually give you their (expert) opinion without any fuss. http://www.sothebys.com/about/contact/as_estreq.html

Answer 2

Judaism - original (kind of) Christianity - derived from pre-Judaism Islam - derived from Christianity and Judaism Hinduism - original Buddhism - original