Here are listed all the sources used. It is always important to choose good sources. Try to use high resolution images and think about the composition, perspective, colors...
The sources are some of the most important pieces in this puzzle.
Masking the car. Use the quickmask mode to select the car and create a new layer mask to mask it.
Remember, in quick mask mode the red areas are not selected and in the layer mask white is for the visible areas and black for the hidden ones.
Place the car. Pick the layer with the car (with the layer mask) and place it over the layer with the field.
Choose carefully the final position to match the perspective.
Place the road. Use the quickmask mode to select and create a layer mask, use the grass brush to refine the mask on the road borders. Transform the road to make it match with the field perpective.
Car shadow. Once you have the car and the road placed you have to add a shadow under the car.
Create a levels adjustment layer and add a layer mask to create the shadow. This shadow must be diffuse, therefore the layer mask edges must be blurred. Select the shadow area and apply a gaussian blur or feather the selection (select>modify>feather) before fill the layer mask with black.
Complete the wheels. Look at the car source to see which parts you can use to make some new ones. Used the car spare wheel to complete the right rear one. Copy and paste the spare wheel area to complete the right rear one and use the clone stamp tool to make it believable.
Sensation of movement. Select the wheels (not the spare wheel) and use the motion blur (filter>blur>motion blur) to apply a vertical blur and give the feel of movement. Try with different values to get the desired result.
Masking the home. One more time use the quick mask mode to select the house and then create a mask for this layer.
This is the best way to keep the source image without modifications.
If you want to make some changes later you can modify the layer mask to show hidden areas of the image. If you erase the image you will have to reload and mask it again.
Draw the bottom of the house. Use the vanishing point filter (filter>vanishing point) to draw with the correct perspective.
Exhaust pipe hole. Make the exhaust pipe hole using the elliptical marquee tool and make a gradient with the appropriate colors. Use blur tool to blur the edges.
Place the house. Pick the layer with the house (with the layer mask) and place it over the layer with the field.
Choose the final position taking care of matching the perspectives.
The chains. Now you have to create a new brush, how? It´s easy, draw this shape to create a couple of links. You can add some dust and dirt to this links, but in this case it is not very important, the chain will be far away and those details will be not visible.
Once you have the links go to edit>define brush preset and voilà, you have your new brush.
Brush presets. Now use the brush presets to improve your brush. Use brush tip shape>spacing to adjust the spacing and useshape dynamics>angle jitter to adjust the direction, use direction control of angle jitter. In this way you will get your perfect chain brush.
Chains. Now is time to use your brand new brush.
Choose the right size for each chain, in this way you will give them depth.
Sketch the blocks. The sketch will help you to draw the concrete blocks.
Concrete blocks.Use various shades of gray to make the block sides with different shadows. Use the blur tool to blur the edges.
Final adjustments and end result. Finally, apply some levels adjustment, add a photo filter and some shadows.
Use the high pass filter to sharp. Use ctrl+alt+shift+E to merge all layers in a new layer, then filter>other>High pass, set the blend mode for this layer to overlay.
I hope you like this tutorial and have learned something with it.