Stereoviews consist of two nearly-identical images, each taken a few inches to the side of the other. When viewed through two lenses set 2½-inches apart, approximately the space between the eyes, the result is the illusion of a three-dimensional image. They generally consist of two photographic images pasted onto a 3½-inch by 7-inch card, although earlier ones were sometimes images on glass.
They became popular first in Europe in the 1850s, followed by the US in the 1860s. Until the 1880s, most of the photographic images were created using wet plate negatives printed on albumen paper. From the 1890s, dry plate negatives printed on gelatin silver paper were produced by large companies, such as Underwood & Underwood in the US, or the London Stereoscope Company in the UK.