Tips about how I made the Frog wallpaper (see wallpaper).

Frog - making of - Step 1

Start with new document, fill background with solid green color.

Frog - making of - Step 2

Apply the following layer effect - Gradient overlay, 150%, white-to-black, radial, blend mode = color burn, effect opacity = about 25-30%

Frog - making of - Step 3

Set foreground color to very dark green (almost black but not entirely), select Pen tool, and start drawing very thin curve...

 
Frog - making of - Step 4

...looking like this.

Frog - making of - Step 5

Resize the curve (Ctrl-T) so that it take a bit more than half of image.

Frog - making of - Step 6

Duplicate this vector many times similar to shown here. There are several ways to do so. One way is to select path with Path Selection Tool (A) and hit Down arrow while holding Shift and Alt keys.

Frog - making of - Step 7

When ready, duplicate this set of shapes and flip them horizontally.