The file we are going to use has Photoshop filter effects that GIMP cannot handle, so unfortunately you will need Photoshop to follow these steps, or at least a friend who has Photoshop!
Read the Read the article from the following link:
http://spin.atomicobject.com/2011/03/07/photoshop-template-forios-buttons/
The article points to some other sources of information, but for now just download this file:
http://spin.atomicobject.com/assets/2011/3/7/iOS_Buttons.psd
Open the file in Photoshop (it may open automatically).
In the Layers palette hide the layers named Background and Tool Bar – Retina.
Expand the layer named Bar Button – Retina, and hide the Button Label layer.
Use the Marquee tool to select an area around the upper right-hand side button. It should now look like the following:
Choose Copy Merged from the Edit menu.
Select New from the File menu, make sure the Background Contents are set to Transparent, and accept the size you are...