Examine the sleeve. The sleeve for the original pressing of the "White Album" is a gatefold with the openings on the top of the sleeve, not on the sides. Later pressings have the openings on the sides. The text "The Beatles" should be embossed, not printed, on the front cover. The sleeve should also have a number stamped on it. Each copy of the original pressing was numbered. Generally speaking, copies with lower numbers are more valuable. If the number is absent, it's a reissue.
Take both disks out of the sleeve and examine the labels. The original pressing of the "White Album" uses the original Apple Records logo, the outside of a green apple on the A side of each disk and an apple cut in half on the B side. The Apple Records label for the original pressing should also have the Capitol Records logo on the outside edge of the b-side label. Other labels indicate later or foreign pressings.
Find the catalog number on the right-hand side of the label. The catalog number for the first U.K. pressing is PMC 7067/8 for the mono edition and PCS 7067/8 for stereo. The first American pressing has the catalog number SWBO 101. The record was not released in mono in the United States.