You may have heard of someone finding a valuable painting at a thrift store or yard sale. You may have also watched "Antiques Road Show" and watched as someone discovered that the old painting or portrait he was keeping in a dusty corner of the attic was painted by a master or was of someone quite famous and actually worth a tidy sum. Learning how to appraise pictures or paintings that you come across will enable you to spot those dusty masterpieces.
Look at the picture, carefully making special note of the canvas or paper. Areas to observe include the age of the work, the signature, and any marks such as numbers or letters on the back of the canvas. With old photos you should also look for signs of age as well as any marking, including a stamp naming the studio that took the photo. It is important to understand that forgeries are common and can be quite convincing, especially to an untrained eye. There are labs that can perform tests on a canvas in order to date the work.
Place the work in context in terms of the school of art as well as the interests in that artist at a given time. Consider the possibility that it was produced by a student rather than the artist himself.
Determine the value of other works by that artist. If you were looking to appraise a work by Monet, you should research how much a comparable painting in terms of size and even subject matter has sold for recently. In some cases, however, a smaller work might prove more valuable based on its relevance to an occurrence or time period in the artist's life.
Have your picture appraised by an art scholar or aficionado, which could include a professor who specializes in a particular school of art or artist. They can confirm or refute your own evaluation. Check with art house appraisers, local galleries and auction houses. It is best to have someone appraise a picture who understands you are not looking to sell it, simply to have it appraised.