Skip to content

Redacting Personal Data – don’t use the highlighter tool!

  • by

Sometimes you might want to send a screenshot to someone, or post it online, but there’s personal data on view you don’t want to share. So you scribble over the words with iPhone’s built-in annotation tools to cover it up. Problem solved! Right?

In actual fact, you have to be very careful when censoring or redacting information in this way. It’s not difficult for somebody to make a few image edits and figure out what the original text says. Let’s see an example…

Above, we’ve redacted some passwords using the annotation tools that come up when you take a screenshot. At first glance, it might look pretty secure – but in some cases the text data is still there, ready to be coaxed out with a few basic image tweaks.

To see for yourself: in the Photos app, press Edit and then tap the Adjustments button for manual controls. Dial exposure to +100 and contrast to -100 and you’ll quickly see that the highlighter and pencil tools – even after lots of scribbling – are easily bypassed. Zoom in and these passwords are very easy to discern. That’s because those drawing tools are partially transparent, even when layered up.



This means anything you post online could potentially be uncovered if you’re not careful. But you may have noticed that the pen and rectangle tools give fully opaque cover that stands up to manipulation. So if you have important data, these are your best tools to use – although be careful with the pen tool, as it’s not as precise as a well-placed black rectangle.

Redaction with a rectangle

So how exactly do you add that handy censor bar?

Take a screenshot and tap the thumbnail in the corner to immediately edit it. Press the + button in the lower right and tap one of the shape icons on the pop-out menu. The rectangle is the easiest way to cover text but any shape will work. You’ll see a hollow rectangle you can resize with the blue handles and move around by dragging with your finger. The final step is to completely fill the rectangle by tapping the shape options button in the lower left and choosing the fill option.

One final note: you might be tempted to use a bespoke annotation app to take your redaction efforts even farther with pixelation and blur effects. These certainly look more professional, although be wary that anyone with access to the right machine learning algorithms may be able to ‘reverse engineer’ even pixelated or blurred text. But nothing can crack open a plain black box!