Cover art is uncredited and appears to be composite based on model sheets.
Reprint information from Inducks and the unofficial Pixar Wiki entry on Buster. The latter also suggests that Speck is the same dog seen as a puppy at the end of the first Toy Story film and called Buster in Toy Story 2. Credits in book do not include full names and were confirmed by writer Jack Enyart and Inducks website.
Reprint information and credits from Inducks website.