The author of this tutorial is Alvaro Salazar Chacon.
The AKVIS SmartMask plug-in can be used to change the background of an image (the following example the sky) regardless of the complexity of objects in the landscape.
Step 1. Open the image you want to edit in Adobe Photoshop.
Original Landscape Image
Step 2. Copy the background to a layer (Layer -> New -> Layer via Copy), so that the plug-in can be used.
Layers Palette
Step 3. Open the plug-in using AKVIS SmartMask: Filter -> AKVIS -> SmartMask.
AKVIS SmartMask Plug-in's Workspace
Step 4. In Sharp mode, use the blue pencil - Keep Area Pencil, - to outline objects you want to preserve. Use the red pencil - Drop Area Pencil - to outline ares of the image that you want to delete.
Selecting Areas in Sharp Mode
After pressing the button, the image will be displayed with two overlying areas, one in red and the other in blue.
Color Areas In Sharp Mode
To see the processing result on a transparent background, press the button. You can hide the strokes ( button) and color regions ( button). The fragment was selected well, but there are still complex areas from the original background.
Result After Processing In Sharp Mode
Step 5. To make a more accurate selection switch to Soft mode.
Soft Mode
Use the green pencil - Transition Area Pencil - to mark areas which are in the background and press the button.
Color Areas In Soft Mode
The result is much better but there are still areas that I want to remove.
Result After Processing In Soft Mode
Step 6. To edit the fragment by hand, switch to Complex mode.
Complex Mode
Use Zoom to enlarge problem areas.
Enlarged Fragment
Use the Drop Colors tool and the Keep Colors tool to add colors to the respective lists. Then select the Magic Brush tool and use it on the image.
Using The Magic Brush
To improve the result further, click on the Foreground Recovery check-box and choose the color black:
Re-treat areas with the Magic Brush (Magic Brush) . The fragment looks perfect.
Restoring Some Of The Object's Color
Step 7. Apply the processing result by pressing the button and the image will be returned to the graphics editor.
Now you can create landscapes with different backgrounds:
, - to outline objects you want to preserve. Use the red pencil - Drop Area Pencil 
- to outline ares of the image that you want to delete.
button, the image will be displayed with two overlying areas, one in red and the other in blue.
button. You can hide the strokes (
button) and color regions (
button). The fragment was selected well, but there are still complex areas from the original background.
- to mark areas which are in the background and press the 
to enlarge problem areas.
tool and the Keep Colors 
tool to add colors to the respective lists. Then select the Magic Brush tool 
and use it on the image.
button and the image will be returned to the graphics editor.
— Changeable Landscape