How to add realistic shadow to your pictures with Photoshop ?

It is so easy to add realistic shadow to your pictures with Photoshop . I had used a picture designed by Illustrator to be clear and easy .

How to do it .

1. Select the shape with the Quick Selection Tool ,or with the color range .
2. Cut the shape and paste it to new layer,and name it picture . 
3. With the Paint Bucket Tool, fill the space of cut picture with black . Select the black shape and cut it also.
4. Add new layer above the background layer and paste the black shape to it.Name the layer with shadow.  
5. Select the  background layer in the layer panel, then clean the picture and fill the space of cut with the same color .[ in the background layer]
6. Select the  shadow layer and apply Transform - Distort .[ Edit - Transform - Distort ].
7. From the layer panel, add layer mask to the shadow layer .Then add gradient overlay.
8. Blur the shadow [Filter -Blur -Gaussian Bur].
9. Reduce the layer opacity and fill  in the layer panel 
10. Save your work.