However not everyone knows how to make the image, it's really easy though.
As a suggestion I wouldn't save this image anywhere but a personal flash drive or in a password protected folder, since it could be used to help falsify your identity. You could sign it differently from your written signature and keep track of when you used it, you'll always know which is which and if you signed the document that way, plus if anyone gets the file they'll not be able to hand forge your signature with it.
- A scanner or camera with macro
- A pen and paper
- Photoshop or Gimp (instructions for both included)
- A PDF editor
Step 1: Write and scan
Now if you're scanning, use black and white mode, I used photo preset but document will likely work fine too.
Save the file somewhere.
If you're taking a photo of the signature make sure it is in focus, evenly lit and from a perpendicular angle to the paper.
For the photo takers, use black and white.
Step 2: Open and crop
Clean up any dirt marks with a white brush.
For photoshop use the crop tool (c) and pull the box down around the signature you want, rotate as needed.
For gimp use the selection tool then go to image>crop to selection