Artist Unidentified.
Title: Nelson Monument Trafalgar Square/Le Monument de Nelson, Place Trafalgar a Londres. 
Signed and Titled in the plate: London, J. T. Wood. 33. Holywell St. Strand. Nelson Monument Trafalgar Square/Le Monument de Nelson, Place Trafalgar a Londres. Presumably, Joseph Thomas Wood published bilingual cards for international visitors of the Great Exhibition 1851.
Dimensions: 4 1/2" x 6".
Publisher: Joseph Thomas Wood, leading printer, publisher, books and stationery seller of Victorian Era.
Date: Circa 1851.
Materials and Techniques: Steel line engraving on "enamel card." Another name is "porcelain card."
Condition: Slight surface abrasion. A detailed condition report is available on demand.
Museums and Libraries: The British Museum and V&A Museum keep several J. Wood's cards.
Note: There is more about J. T. Wood in the informative post "J. T. Wood of the Strand" by Laurence Worms  (Ash Rare Books) in his blog "The Bookhunter on Safari."