I finally found out how to set the <kbd>Clone</kbd>.

<br/>

## Steps

The following step is under **Blender 2.77a** in **Ubuntu**.

1. Go to `Texture Paint` mode.

   [![enter image description here][1]][1]

1. According to the following image, you can click <kbd>Brush</kbd> -> <kbd>Image Paint Tool</kbd> -> <kbd>Clone</kbd>.

   [![enter image description here][2]][2]

1. Set the `Brush` to clone.

   [![enter image description here][3]][3]

1. Go to `Option` and configure the setting like the following.

   [![enter image description here][4]][4]

1. Go to `Slots` and select the `Paint Mode` as `Image`.

   [![enter image description here][5]][5]

1. Create a new `Canvas Image` and rename it as what you want. e.g. `Casper Texture`.

   [![enter image description here][6]][6]

1. Set the `UV Map` you want to paint it to.

   [![enter image description here][7]][7]

1. Check the checkbox `Clone from image/UV map`.

   [![enter image description here][8]][8]

1. Select the `Source Clone UV/Map`.

   [![enter image description here][9]][9]

1. Select the image of the UV/Map you want to clone.

   [![enter image description here][10]][10]

1. Paint it.

   [![enter image description here][11]][11]

1. Save your painted UV/Map image.

   [![enter image description here][12]][12]


<br/>

## References
* [Blender - "Micky" Ch.1 - Pt. 9 - Texture painting with Clone Brush](https://www.youtube.com/watch?v=DooeJwglbDU)


  [1]: https://i.sstatic.net/FlpFX.png
  [2]: https://i.sstatic.net/00RUP.png
  [3]: https://i.sstatic.net/KFRpu.png
  [4]: https://i.sstatic.net/oqUVe.png
  [5]: https://i.sstatic.net/Kiqur.png
  [6]: https://i.sstatic.net/mCQeM.png
  [7]: https://i.sstatic.net/SQkgr.png
  [8]: https://i.sstatic.net/wSJDi.png
  [9]: https://i.sstatic.net/RpFC6.png
  [10]: https://i.sstatic.net/MQXTv.png
  [11]: https://i.sstatic.net/7YfUp.png
  [12]: https://i.sstatic.net/rMfXz.png