MLA

Robert Devereux, Earl of Essex from an Original Picture in the Collection at Strawberry Hill. [Graphic]. Publish'd 6 Octr. 1798 by S. Harding, 127 Pall Mall, & P. Brown, Crown St., Soho, 0AD. https://collections.library.yale.edu/catalog/16193394.

APA, 6th edition

Robert Devereux, Earl of Essex from an original picture in the collection at Strawberry Hill. [graphic]. (0 C.E.). [Portrait prints, Stipple engravings England London 1798]. Publish'd 6 Octr. 1798 by S. Harding, 127 Pall Mall, & P. Brown, Crown St., Soho. https://collections.library.yale.edu/catalog/16193394.