more info at http://getgreenshot.org/help/

Obfuscating things

Obfuscating parts of a screenshot is a good idea if it contains data which is not
intended for other people to see, e.g. bank account data, names, passwords or faces on images.

Use the obfuscate tool O exactly like the highlight
tool.

Available options for obfuscation are:

• Pixelize: increases the pixel size for the selected area
• Blur*: blurs the selected area

* Depeding on the performance of your computer, applying a blur effect might slow down
Greenshot’s image editor. If you feel the image editor reacting slowly as soon as a
blur is applied, try reducing the value for Preview quality in the toolbar or
decrease the value for Blur radius.

If the blur performance is still too bad for you to work with, you might prefer
to use the pixelize effect instead.