It is wrong to draw on photographs.
Thomas' grandmother was showing him her old wedding photograph's and talking about missing his departed grandfather.
Thomas wants to make a gift for his grandmother.
Thomas redraws his grandmother's wedding photograph and writes her a lovely letter.
Thomas gets the black and white photograph of his grandmother and colors it with his pencils.
Thomas's grandmother is happy to receive the drawing and thanks him for his thoughtful gift.
Thomas's grandmother is shocked and saddened at what Thomas had done to her wedding photograph.