How to blur part of an image, not the whole picture

Blurring the whole screenshot is how you get a useless rectangle. You want one region dead and the rest readable.

Support tickets, bug reports, and “can you believe this chat” posts all fail the same way. Someone applies a filter to the entire PNG because the editor’s blur is a slider, not a box. Recipients cannot see the error. The secret might still be guessable at the edges. Partial cover is the whole skill.

How do I blur only part of a screenshot?

In any decent editor you drag from one corner of the secret to the opposite corner. Include padding. A letter that sticks out of the blur is a clue. Release. Look at 100% zoom. Undo if the box is short. Repeat for the next secret instead of growing one giant fog.

On BlurThis that is the only drawing gesture: press, drag, release. Switch to a bar when the region is a phone number or an OTP. Blur is optional cosmetics for a messy desktop. The gesture stays a rectangle.

Why not blur the entire image?

Because then you have no evidence. A manager cannot see the broken button. A teacher cannot see the quiz question. A friend cannot see why the chat was funny. Full-frame blur is a way to feel private without doing the work of locating the secret. Locate it. Cover that.

Full-frame blur is also a weak privacy move if it is light. You still leaked layout, app chrome, and maybe readable headings. Heavy full-frame blur is just a wasted capture. Crop or do not send.

Several secrets in one shot

Do not make one giant fog over the window. Make three tight covers: chat name, phone, quoted reply. Readers can still see the bug you are reporting. Inbox list views need a bar per row you cannot crop. Gmail is famous for this: you meant the one thread, the list still prints five other subjects.

Sidebars are their own region. Slack workspaces, Teams org names, Discord servers. If the sidebar is not part of the story, crop it at capture time. If you already captured, bar the strip. Do not “soft blur” a column of emails.

When is crop enough instead of a box?

If the secret is only in a corner, cut the photo. Menu bars, taskbars, keyboards, notification banners. Crop cannot save you if the email sits between two paragraphs you must keep. That is what a bar is for. Crop versus bar is the longer fork in the road.

People crop too tight and clip the error code they needed. People crop too loose and keep the account switcher. Check once at the actual pixel size, not in a tiny preview in the composer.

What if the secret is a phone number or email?

Treat those as bars, not light blur. Cover the digits, the country code, the formatted spaces, and the repeats in headers and quotes. Details: hide a phone number or email. Partial cover fails when you bar the bubble and leave the header.

Irregular shapes

You rarely need a freehand lasso. UI is rectangles. Faces in a group photo are the exception, and even then a box with padding is easier to verify than a “clever” ellipse that misses an ear and a name tag. If you must cover a non-rectangular control, use overlapping rectangles until the glyphs are gone. Overlap is cheaper than a leak.

Watermarks and stamps that sit on top of an image in another app can be layers. Flatten. A box you drew in a slide deck might still be an object someone can move. A downloaded PNG from a canvas is pixels. Send that object.

Undo exists so you can tighten a box. Use it. A first drag that clips a digit is worse than a second drag that looks slightly ugly. Ugly bars are honest. Pretty short bars leak.

A tight-box checklist

• One region per secret, with padding.
• Headers and quotes get their own boxes.
• Zoom in. If you can guess a character, enlarge the cover.
• Export PNG. Send the export, not a photo of the editor.

Partial redaction looks like more work than a full-image filter. It is less work than explaining a leak, and it leaves the actual screenshot useful. Drag the box. Stop there.