This is a lovely shot from the Dreams of Spanking site. There’s a lot of humor and fun in those sly smiles. The use of the mirror to capture both his and her expression while keeping a natural feel to the composition is cleverly done. From the look of that red bottom I’d guess this was taken in the middle of a scene.
You can see the larger version of the image, together with other shots from the same scene here. It’s actually a foursome in the full scene shots.