A few words about history of illustration.

Illustrations can be used to display a wide range of subject matter and serve a variety of functions like:

• 1. giving faces to characters in a story
• 2. displaying a number of examples of an item described in an academic textbook
• 3. visualizing step-wise sets of instructions in a technical manual
• 4. communicating subtle thematic tone in a narrative
• 5. linking brands to the ideas of human expression, individuality and creativity
• 6. inspiring the viewer to feel emotion in such a way as to expand on the linguistic aspects of the narrative

Early history

The earliest forms of illustration were prehistoric cave paintings. Before the invention of the printing press, illuminated manuscripts were hand-illustrated.

15th century through 18th century

During the 15th century, books illustrated with woodcut illustrations became available. The main processes used for reproduction of illustrations during the 16th and 17th centuries were engraving and etching. At the end of the 18th century, lithography allowed even better illustrations to be reproduced. The most notable illustrator of this epoch was William Blake who rendered his illustrations in the medium of relief etching.

Early to mid 19th century

In the early 19th century the proliferation of popular journals, which often serialised novels for mass-circulation, produced a boom in popular illustration. The medium moved away from steel engraving which was the standard in the early century towards wood-engraving which could more easily be incorporated into pages of text. Book and journal publishers would employ workshops of wood-engravers to render artists’ drawings onto polished blocks of fine-grained yew or box-wood which could then be locked directly into the printing-chase with the metal type. Notable figures of the early century were John Leech, George Cruikshank, Dickens’ illustrator Hablot K. Browne and, in France, Honoré Daumier. The same illustrators would contribute to satirical and straight-fiction magazines, but in both cases the demand was for character-drawing which encapsulated or caricatured social types and classes.

The British humorous magazine Punch, which was founded in 1841 riding on the earlier success of Cruikshank’s Comic Almanac (1827-1840), employed an uninterrupted run of high-quality comic illustrators, including Sir John Tenniel, the Dalziel Brothers and Georges du Maurier, into the 20th century. It chronicles the gradual shift in popular illustration from reliance on caricature to sophisticated topical observation. These artists all trained as conventional fine-artists, but achieved their reputations primarily as illustrators. Punch and similar magazines such as the Parisian Le Voleur realised that good illustrations sold as many copies as written content.

Source: wikipedia.org, answers.com