How to extract Preview's signatures for use in other applications

The Preview application in OS X has an excellent option for capturing handwritten signatures and inserting them into PDF documents. This is great for signing forms, letters, and other items that require a signature. The process for doing so simply involves capturing a written signature with a Web cam, after which you can append them to any PDF document open in Preview.

Signatures that you associate with Preview in this manner are stored in an encrypted form, which is great for security but also means that Preview is the only program that can access them. Even though an inserted signature is resizable and can be moved around in the given PDF document, you cannot copy it or a selection that contains it from Preview to another program.

One solution to this is to simply scan your signature in and save it as an image, but this requires you have a scanner handy. However, there is a workaround you can use that will allow you to capture any signature from Preview and save it as an image file with proper transparencies that you can use in other applications.

First be sure you have a signature captured and stored in Preview, which can be done by following the instructions provided by CNET's Jason Cipriani, then perform the following steps:

1. Open a text editor such as TextEdit, Pages, or Word, and create a new blank document.
2. Press Command-P to print the blank document and choose "Open PDF in Preview" from the small PDF menu in the lower left.
3. Enable Preview's Edit toolbar (press Shift-Command-A), and use the Signature tool to add a signature to the document.
4. Expand the signature size to be relatively large (the larger the better, which can also be done by zooming in on your document and expanding its window size).
5. Press Shift-Control-Command-4 to enter selection-screenshot mode (your mouse cursor will turn into a crosshair), and drag a selection around your signature (when you release the mouse you should hear a camera click).
6. Ensure Preview is the foremost application and press Command-N to create a new image file from the screenshot.
7. Enable Preview's Edit toolbar again, and select the Instant Alpha tool (it looks like a little wand).
8. Click the white area around the signature and drag your cursor away from where you click. When you do this the white area will turn pink, but keep dragging until you do not see any more white around the characters of your signature. If the characters themselves show a pink hue then you have dragged too far so back off a little until they turn black again, followed by releasing the mouse button.
9. Press the delete key, and your signature should now be on a transparent background indicated by a checkerboard pattern.

Save the image in a format that supports an alpha channel (PNG, JPEG-2000, or TIFF), and ensure this channel is enabled in the Save dialogue box so the transparency is preserved.

There you have it. You should then be able to import the signature into any program that supports the formats you saved it in. Do keep in mind that, unlike Preview's signature management, this is not an encrypted storage of your signature; however, you can save it in an encrypted disk image, or keep FileVault enabled on your Mac so all files including the signature are encrypted when your system is shut down.

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