Autumn leaves - making of - Step 18

Now merge all layers (Ctrl-Shift-E), it is a good idea to save a copy of PSD file before that. For resulting single layer, open layer effects, and add Gradient overlay:
- blend mode = linear burn;
- opacity = about 20%;
- gradient = white to black (reversed);
- style = radial;
- scale = maximum.

This will give us nice fading effect, where image is darkened at the edges.

Autumn leaves - making of - Step 19

I thought it is nice touch to add subtle water drops to the image. Here is how to create them: make new document, pretty small (100x60 pixels as example). fill with grey.

Autumn leaves - making of - Step 20

Go to Filters - Noise
 
- Add noise, apply very big noise (200%).

Autumn leaves - making of - Step 21

Here goes tricky part:
- switch to quick mask (Q)
- repeat noise effect (Ctrl-F)
- turn off quick mask (Q)
- delete selection (Del).

Autumn leaves - making of - Step 22

Repeat previous step again...

Autumn leaves - making of - Step 23

..and again, until black dots are not too close to each other.

Autumn leaves - making of - Step 24

Resize image to match the size of our wallpaper (for me it was about 1000%).