Examine the surface of the work. On an original painting, the paint should be thicker and rise off the canvas in places where colors are layered on top of each other. On a print, all areas are flat.
Touch the surface of the work carefully. On an original painting, you will feel changes in texture, from bumpy to smooth, that have been caused by individual brushstrokes. The surface of a print will feel uniformly smooth.
Look closely at the brushstrokes. In an original painting, the brushstrokes will follow the contours of the images. Some prints have fake brushstrokes applied mechanically to add texture, but these brushstrokes won't follow the logical contours of the painting.
Hold the work up to a light source. On an original painting, you might see pencil marks that were made by the artist before she started painting. You might also see other shapes that started out as part of the painting but eventually got painted over. It's more likely to be a print if you can see the entire image clearly and uniformly.
Use a watchmaker's loupe or strong magnifying glass to look at the colors up close. If you see a pattern of overlapping colored dots of cyan, yellow, magenta and black, this indicates that the image was produced by a printer and is therefore not an original painting.
Look for a series of numbers along the edge of a piece. Fractions like "3/50" indicate a limited-edition print, where the "50" indicates the total number of prints produced in the print run and the "3" indicates the order number of that particular print. Prints might also display a copyright symbol and date.
Check the back of the work. Original paintings often have a label with information about the work, such as the artist's name, title of the painting and registration number.
Examine the edges of the canvas. If you see rough threads along the sides, it's more likely to be an original painting. Factory-made prints done on paper, cardboard, fiberboard or polystyrene do not contain these imperfections.
Consult an art expert like an appraiser, art collector, or museum curator if you're still unsure.