~/challenges/unblur$ rwx.sh

Blurring, as a tool for obscuring personal information in images, is both ill-advised and exceedingly common.

Screenshot blurred using GIMP 2.8's Gaussian blur tool, 8px radius.

One especially bad choice is box blur on monochrome text. Consider a 7×7px box blur:

Monochrome text, 7×7px box blur.

A more popular choice of blur is pixelization, in which the image is divided into a grid and each grid square is filled with its average value. Unlike box blur, pixelization is not invertible for monochrome images. However, it is still easy to recover text because a only a few bits of information are required to deduce each character when the character set is known.

6×6px pixelization.

Courier New 11px.