|- Example ; that white & pink layer -|
1 . You better make your photos background transparent. Refer this tutorial : Tutorial transparent photos using Gimp
2 . Open your Gimp 2 software and open photos that you want.
3 . Right click > Filters > Light and Shadow > Drop shadow
4 . A pop-out window will appear so you just have to adjust Offset X , Offset Y , Blur radius , Color and Opacity as you want. When you have adjust them, click ok.
5 . Done with the layer / shadow, save your photos. Good luck :)