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How to Unblur a Screenshot: What Can Really Be Recovered

Name: Pizazoo
Author: Pizazoo

Can a blurred or pixelated screenshot be unblurred? What research recovers, why highlighter marks leak, and how to redact safely on iPhone and Mac.

October 6, 20268 min read

Muhammed BasilFounder & maker of Pizazoo

You can't truly unblur a screenshot. Blur and pixelation throw information away, and no app puts the original pixels back. But researchers have shown that blurred or pixelated text can often be guessed back by rendering candidate text in the same font and matching the result, and see-through highlighter strokes can be lifted with a brightness edit. A fully opaque box or a crop is different: those pixels are gone for good.

Below: what can and can't be recovered, then the safe way to redact on iPhone (iOS 26 and iOS 27) and Mac (macOS Tahoe 26 and macOS 27).

Can you unblur a screenshot?

Not in the way "unblur" apps suggest. Blurring averages each pixel with its neighbors, and pixelation (also called mosaicing) replaces each block with one average color. A 2016 study from UC San Diego puts it plainly: both are lossy, so they "cannot, in general, be reversed to recover the original image" (Hill et al., PoPETs 2016).

The catch is in the same paragraph: text is predictable (a known font, a small set of characters, real words), so enough information can survive to work out what it most likely said. That is guessing and checking, not unblurring, and it works best on exactly what people hide: email addresses, account numbers and short codes.

Can pixelated text be recovered?

Often, under the right conditions. Three well-documented projects show how:

Depix (2020). A proof of concept by Dutch security consultant Sipke Mellema. Because the original information "is lost, it is impossible to directly reverse the filter", Depix pixelates a reference image of known characters in the same font and looks for matching blocks (Synced Review). Its documentation lists the limits: it needs the exact font and screen settings, text drawn on whole-pixel positions, and it degrades when the image has been recompressed (Depix).
Unredacter (2022). Security firm Bishop Fox built it, citing research that found Depix struggles with real-world images. It guesses the hidden text one character at a time and compares each guess with the pixelated block, assuming it knows the font and size, which an attacker can usually read from the unredacted text nearby (Bishop Fox).
The 2016 PoPETs study. Using hidden Markov models (the statistics behind older speech recognition), the researchers recovered short and long passages of mosaiced text, decoded real examples posted online, and still got readable text from images degraded by heavy JPEG compression (Hill et al.).

Bigger blocks make it harder, not impossible. The same study recovered English sentences set in an 18-pixel font and hidden under 24-pixel mosaic blocks.

Can blurred text be read?

The same research covers blur. The PoPETs team extended their method to Gaussian blur, the common blur filter in photo editors, and concluded that "mosaicing and blurring, despite their widespread usage, are not viable approaches for text redaction." A separate 2016 paper trained neural networks to recognize faces, objects and handwritten digits through pixelation and YouTube-style blurring (McPherson, Shokri and Shmatikov).

Light blur over large text is the weakest cover. Heavy blur over small text is stronger, but nothing in this research points to a blur strength you can rely on for text.

Do AI unblur tools reveal hidden text?

No. AI enhancers sharpen what is there and invent what isn't. Duke University's PULSE project, which turns very blurry faces into sharp portraits, is the clearest example: its researchers say the system "cannot be used to identify people" and instead generates "new faces that don't exist, but look plausibly real" (Duke University). Text works the same way. Feed an enhancer a blurred account number and it will output crisp digits, but they are a plausible guess, not a recovery.

How can someone see through red markup in a screenshot?

When the markup is translucent. The Marker (highlighter) in iPhone and iPad Markup is designed to tint text, not hide it, so each pixel under a stroke is a blend of the marker color and whatever is underneath. Push exposure, brightness or contrast far enough and the difference between "marker over letters" and "marker over background" shows up again. In 2019, a widely shared demonstration did exactly that with edits to exposure, highlights, shadows and contrast in Photos, and several passes with the marker did not fix it (TNW, AppleToolBox). The color doesn't matter: red, black or yellow, any stroke below full opacity can leak.

Use this to check your own work. Before you share a marked-up screenshot, open it in Photos, tap Edit, tap Adjust, and drag Exposure and Brilliance up (Apple, iOS 27). If letter shapes appear, tap Cancel, then Discard Changes, and cover the area properly. A fully opaque cover replaced those pixels, so there is nothing for the sliders to bring back.

Can blacked-out text be uncovered?

Not from the pixels. If a fully opaque box covers the text in a flattened image, the original pixels are gone, and no filter, app or AI can bring them back. When blacked-out text does leak, it is through something other than the box:

The cover is see-through. Translucent marker strokes or a fill with reduced opacity (see above).
The original traveled with it. Photos on iPhone keeps the original under every edit, and you can return to it with Revert to Original (Apple). A normal share sends the edited version, but turning on All Photos Data in the share sheet's Options sends "the original file with edit history and metadata", and the recipient can modify the current version (AirDrop only) (Apple).
The editor left old data in the file. In 2023, the "aCropalypse" bug showed that Google Pixel's Markup tool left part of the original image at the end of edited files, so cropped or redacted areas could be partly recovered (BleepingComputer). The Windows 11 Snipping Tool had the same flaw (BleepingComputer). Both have been patched, but BleepingComputer noted that Pixel images shared before the fix remain vulnerable.
The box is an object, not pixels. Apple notes that annotations on an image file can't be edited after you save it, while annotations on a PDF stay editable (Apple). Editable means anyone can select the box and delete it. The same goes for a rectangle placed over a screenshot in a slide or document.
The bar's size gives it away. At the Eurocrypt 2004 rump session, researchers used font measurements to work out which of a short list of candidate phrases fit a blacked-out gap, and other work found traces of redacted text in nearby JPEG compression artifacts (both summarized in Hill et al.). Make bars a little larger than the text, or crop.

How do I remove markup from a screenshot on iPhone?

If it's your own screenshot and you added the markup in Photos, open it, tap the More button, then Revert to Original (Apple). If someone sent you a marked-up screenshot, the markup is baked into the pixels you received, unless they AirDropped it with All Photos Data turned on. There is no hidden layer to peel off.

Is blurring a screenshot safe?

Method	Can the hidden text be recovered?
Solid box at full opacity	Not from the image. Its size can hint at the length.
Crop	Not from a correctly saved file.
Pixelate	Often, if the font and size are known (Depix, Unredacter, PoPETs 2016).
Blur	Often, by the same methods.
Highlighter or translucent pen	Yes, with brightness and contrast edits.
AI "unblur" apps	They produce guesses, not recoveries.

A simple rule: blur is fine for decoration, like a face in the background or a busy group chat. Anything you'd mind a stranger reading (passwords, card numbers, one-time codes, addresses, account IDs, API keys) gets a solid box or a crop. The researchers behind the 2016 study go one step further: if you control the source, replace the sensitive text with a placeholder before you take the screenshot, which also hides its length.

How do I redact a screenshot safely on iPhone?

iPhone Markup has no blur tool, but a filled shape is the safer cover anyway. In iOS 27 (iOS 26 works the same way):

Right after taking the screenshot, tap the Markup button in the preview. For an older screenshot, open it in Photos, tap Edit, then the Markup button (Apple).
Tap the Add button (Apple calls it Add Annotations in Photos), tap Add Shape, and choose the square. Drag it over the text and resize it with the dots on its outline, a little past the edges of the text.
In the Markup toolbar, set the fill color to black and leave opacity at maximum (Apple).
Or crop the sensitive part out entirely by dragging the crop handles.
Tap Done, pinch to zoom in on the result, and run the Exposure check above.
Share normally and leave All Photos Data off.

For the pen method and the Photos Clean Up caveats, see how to blur or black out a screenshot on iPhone.

How do I redact a screenshot safely on Mac?

macOS has no blur or pixelate tool in Markup either. In macOS 27 and macOS Tahoe 26:

Click the floating thumbnail after you take a screenshot, or select the file in Finder, press Space for Quick Look and click the Markup button (Apple).
Click Shapes, choose the rectangle, drag it over the text, then click Fill Color and choose black.
Click Done. Apple notes that changes made in a Quick Look window can't be undone after you close it, so duplicate the file first if you need an unredacted copy.
In Preview, the same tools sit in the Markup toolbar, and annotations on an image become permanent once you save (Apple). Redact the image itself, not a PDF made from it.

For a detailed walkthrough, see how to redact sensitive information in screenshots on Mac, and for codes, how to blur a QR code in a screenshot. Our free Redact Screenshot tool also works in any browser: choose Blackout (safest), drag over the sensitive areas, and it exports a PNG that contains only the final pixels, without uploading your image.

How does Pizazoo handle redaction?

Disclosure: we make Pizazoo. The built-in tools above are enough for an occasional redaction. If you share screenshots often, Pizazoo's editors include dedicated redaction tools:

On Mac, the markup editor in Pizazoo (macOS 14 Sonoma or later) includes redact, blur and pixelate tools, plus auto-redaction that finds personal info and QR codes. Before you run Auto-Redact on anything secret, check that its Redaction Style is set to Solid Redact.
On iPhone and iPad, the free Pizazoo app (iOS and iPadOS 17 or later) has a Redact tool with two styles: Blur and Black Bar.

For anything sensitive, pick Black Bar on iPhone or redact on Mac, and keep blur for faces and background clutter. Then do the same zoom-in check before you share.