Johnston was among the early illustrators to realize the significant role that photography could play in journalism.

According to tradition, she asked George Eastman to recommend a camera suitable for press photography. Eastman, founder of the Eastman Kodak Company, had only recently marketed his first Kodak, and he sent Johnston one with his compliments. [Johnston became an agent for Kodak shortly after receiving the camera.]

She studied photography formally under the direction of Thomas William Smillie, head of the Division of Photography of the Smithsonian Institution in Washington. With this training, Johnston bravely launched her own career.

For their illustrations, newspapers and magazines in the 1880s relied heavily on zinc engravings, which were relatively easy for an artist to create from a photograph. In the 1890s the use of zinc engravings declined as a visual medium. In January 1904 the London Daily Mirror became the first daily newspaper in the world to use photography exclusively for its illustrations.