This is such a charming, clever picture. The more you look, the more you see. You can see each individual leaf and crease of the girls dress. Notice her leather shoes and the wrinkles in her stocking. It could be a photograph but the artist makes it a poignant painting, featuring children and death, two important themes in Victorian genre paintings.
Johnson himself was a self-taught artist born in Stratford-le-Bow in 1825 who didn't take up painting full time until he was 38. He was much admired by Birket-Foster (who was also self taught). Johnson exhibited in New York and was very popular, having painted at least 190 pictures by his death in 1896.