Painting from photographs, especially since digital photos can be viewed so clearly on a monitor, can have many advantages over painting landscapes in the field. The benefit is that your composition has been established and your borders defined. You can do all your composition in the viewfinder of your camera which eliminates one major step while painting. A two dimensional photo is also easier to grasp being that you don't have to transpose your three dimensional view in the open into two dimensions on your canvas.
There is no substitute for seeing though and everywhere you go, you must constantly analyze the things you eyes see in real life.
Use your own photos otherwise you will not have the same understanding about the subject even if seeing the real thing was only for a moment.