This is one of the tasks passed to me as an intern for an advertising agency. This is a fun problem to solve. Turns out that the photographer shot a light fixture product upside down. Photoshop to the rescue! (I used CS3) This image is most of the photoshop file. All that’s missing is the product isolated right side up. I created four layers to create the shadows for the product’s new orientation as well as using the ambient shadows from the original photo. I clone-tooled the edges that stuck out beyond the product turned right side up.
I created a few shadow layers starting with a dark silhouette of the product and then distorting those to be slanted at different angles. On few of the shadow layers I used a gradated layer mask, setting the shadow to to multiply and for some a Gaussian Blur. I worked side by side the original photo to capture similar lighting angles. The anchor shadow (the sharper highlight right next to the object, which is normally really dark) was light because the object is shiny and lit in a specific way.
Thinking back on it, Jason Hoppe‘s class lecture on creating realistic drop-shadows is very practical. Teach a person how to photograph, you have shadows of a moment. Teach a person to Photoshop, you have shadows for life!