“Bubbles”, by Sir John Everett Millais was painted in 1885-6. Millais originally titled his painting 'A Child’s World' but it was later changed to 'Bubbles'. The painting with its copyright was sold to A & F Pears, manufacturers of Pears soap. The Managing Director of Pears, Thomas Barrett, was a pioneer of modern advertising methods, and he and William Lever of Lever Brothers, makers of Sunlight Soap, were great rivals, each spending vast sums on promoting their brands.
Barrett turned 'Bubbles' into an advertisement by adding a bar of soap in the foreground. Millais was furious, but he could do nothing about it. Millais was unfairly criticised for degrading his art, but as the copyright owner, Barrett was within his rights. And the use of the painting for advertising meant that the picture became the best known of all his works. 
Lever responded to Barrett’s initiative in 1889 by purchasing 'The New Frock' by Frith and using this to advertise Sunlight Soap, again without the artist’s permission. Frith’s painting and others used for Sunlight Soap advertising, are now part of the Lady Lever Art Gallery collection.
source: http://www.liverpoolmuseums.org.uk/picture-of-month/displaypicture.aspx?id=299
