Removing sensitive information from screenshots, images, or documents is easy—and sharing the result is even easier with Copy as PNG.
Let’s say your image is already on the canvas in OmniGraffle. (Though if it isn’t, just drag the file right on top.)
First, draw a regular old object as close to your final size as you can manage. You can always resize.
Next, using the Fill inspector, set a Distortion Effect—typically using Pixelate with a value of 20 gives off the right impression for a censored image! (Though increase it if the goal is to not give off any impression of the subject.)
Finally, select everything you’d like to share and select Copy As PNG from the shortcut menu. Boom, paste, done.