How to clone background?
I have this picture, where I would like to fill out the green in the top with the background from the picture, so fix that the picture have not been cropped in 4:3.
Can a background like this be cloned?
You could use Photoshop's CS6 (also available in CS5) content aware feature.
Select the part you want to fill with the selection tool.
Shift+Backspace to launch the fill dialog.
Make sure "Content-Aware" is selected under the "Use" part, and you're done.
Tip: To get an even better result, you could use content-aware on the thin line that separates the original background, and the one created using the content aware tool.
Added some photos as example here