Examine a print or painting with a loupe or magnifying glass of at least 10X magnification. Look for tiny dots of equal size uniformly distributed across the picture. These are called Ben-Day dots and indicate the artwork is a cheaply printed offset lithographic reproduction.
Identify the artist by finding a signature. Usually it's in the bottom right-hand corner of a picture, but could be anywhere, including on the back. Check the bottom of a sculpture or art pottery for a signature or stamp of the maker. Research the artist on the Internet or in your local library to get an idea of how their work is priced. Look for similar artworks to compare to yours.
Examine the artwork closely to establish its condition. Check paintings for rips, cracks, or paint flakes. Look for signs of touch-up or repairs such as in-painting, relining, or amateur cleaning. See if the colors have faded from exposure to sunlight or if there is water or insect damage. Peruse prints closely for pinholes or burns from acidic matting or backing materials. Condition significantly affects the value of art.
Compare signatures and styles of known authentic works in art galleries and museums. Try to find out if the artwork is a fake, forgery or derivative work by another artist. Make sure the style fits the date of the painting, if known, as artists often change their style as they develop over the years. Be aware that famous artworks are often copied and that artists sometimes copy very closely the style and technique of well-known artists.
Collect as much information as possible about the artwork to establish its provenance. Ask the sellers where they got it and if they have any documentation such as sales receipts, exhibition records or paperwork indicating the lineage of previous ownership. Check the back of paintings for inscriptions or gallery stickers. Take the artwork to a local museum, university or professional appraiser for an appraisal if it passes all the tests of authenticity.