PSA: iOS Markup is not designed to be a redaction tool for sensitive information

In iOS 11, Markup is a system-level feature able to annotate and draw shapes over images and PDFs. It lets you draw with a pen, a marker and some basic squares and circles over photos. Apple doesn’t really advertise Markup as a redaction feature, to cover up information, but it feels like it is up to the job and I’ve seen many people on social media use it to do just that.

However, you have to be careful as the Markup tools can be deceptive, particularly the marker. Even if it looks like the personal info is obscured, some basic photoshop work easily reveals what is underneath …

Markup offers a pen tool and a marker tool. Using a finger, you can paint over the picture. The pen tool draws a small line whereas the marker has thicker strokes, bigger and wider.

Intuitively, I think the marker is the obvious choice to cover up some text. It takes less strokes to write over a region simply because it’s larger. However, the marker is actually slightly transparent. If you do only one coat, this is obvious. If you do two or three coats, the human eye just sees solid color, and it is reasonable to believe that the content underneath is lost.

This is not true regardless of whether you do one brush stroke with the marker (which is easily transparent) or multiple (when it appears to be solid).