A Boy and His Dog (1851)
by
W. R. Waters
Waters (flourished 1838 - 1867) was an English painter, fairly obscure now.
I have also seen this painting identified as "Portrait of a child wearing a burgundy velvet dress with lace collar and straw hat, holding a riding crop and leaning against a Saint Bernard."
As for the title A Boy and His Dog, that itself may strike some as strange, given the fact the child in the painting does appear to be wearing a dress-like garment, but in 18th and early 19th centuries it was common practice in England to dress male and female children in similar garb until late childhood. The dog pictured here certainly seems more like a Newfoundland than a St Bernard, although it must be remembered that breed standards did not exist until the later 19th century, and there was great variation in what a "St. Bernard" or a "Newfoundland" might look like.