Guide
One sentence carries this page: a scrolling capture is a file you have never seen all of, and the two things that catch people out are the regions below the fold you never reviewed and the sensitive line that the stitching copied into the image more than once.
What a scrolling capture actually is
A full-page capture is not a photograph of a tall thing. It is a composite. The software scrolls the window in steps, grabs a frame at each step, and joins the frames into one image. Browser extensions do it for web pages, phones do it for apps and web views, utilities do it for windows and documents. The result arrives as a single PNG and it is natural to read it as a single view of a single moment. It is neither.
Implementations differ in ways that matter here, and it is worth checking yours rather than assuming. Some detect elements pinned to the window and strip them from all but one frame; some leave them in. Some overlap consecutive frames and blend the seam; some butt them together. Some wait for lazily loaded content; some capture whatever happened to be rendered. The consequence is the same whichever yours does: the finished image can contain content that was never on screen together, and it can contain the same content twice.
A long capture also spans time. Forty screens take seconds or tens of seconds, during which a clock in a status bar advances, a relative timestamp moves from one minute ago to three, a notification arrives, an unread badge changes, a live figure refreshes. Two copies of what looks like the same element can therefore disagree — which both dates the capture and hints at how long you spent on it. For redaction the practical point is that your sense of having dealt with something already is unreliable: the item you covered at the top is not necessarily the same pixels as the item further down that looks like it.
The second copy is what gets people
Ask of every sensitive item: how many times does this appear in the file? On an ordinary screenshot the answer is almost always once, which is why nobody asks. On a scrolling capture it is routinely more, from several directions at once.
• Pinned interface. A header carrying the account holder’s name, a balance floating above a list, a sticky toolbar, a persistent sidebar. If your tool does not strip these, they appear at every frame boundary.
• Seam overlap. Where consecutive frames overlap, the rows inside the overlap are duplicated a few hundred pixels apart — sometimes as a partial row you read past without registering.
• Repeating columns. A long list repeats its own structure: the sender name on every message, the account number on every row of a statement, the same delivery address on every line of an order history.
• Summary and detail. A figure in a header card is usually also a row somewhere further down.
• Chrome at both ends. The top and the bottom of a long capture often both carry an address bar, a tab title, a page footer naming the organisation, or a print header with a URL and a date.
So count before you cover. Scroll the whole file once and write down, for each item, how many instances you saw. Then cover by pattern rather than by position: if an identifier lives in a column, treat the column as the target and put a band across every occurrence, instead of hunting individual cells and trusting that you got them all.
The editor’s view is a window onto a much bigger canvas
The mechanics are worth knowing precisely, because they explain how an unreviewed region ends up in a file you believe you checked. When you load an image, the canvas is created at the image’s exact pixel dimensions — a 1,080 by 12,000 capture becomes a 1,080 by 12,000 canvas. That canvas is displayed inside a panel capped at seventy percent of your browser window’s height, which scrolls, and the canvas is drawn at a maximum width of one hundred percent of the panel, a rule that caps its width but never enlarges it.
Put numbers on that. In the roughly 930 pixels of content width this layout gives you, a 1,080 pixel wide capture is displayed at about 0.86 of its size, so 12,000 image pixels become around 10,300 on-screen pixels of height. If your window leaves the panel 550 pixels, you are looking at a little over five percent of the image at a time, and it takes around nineteen panel-fuls to reach the bottom. Nothing in the interface tells you how much is below, and Download PNG serialises the whole canvas — so what you send is all 12,000 rows, reviewed or not.
One piece of good news. Pointer and touch positions are converted into image coordinates using the canvas’s current on-screen rectangle, recomputed at every interaction, so the panel’s scroll offset and your browser’s zoom level are both accounted for automatically. Covers land where you put them however far down you have scrolled and however far you have zoomed out. Zooming the browser out to get more of a long capture into view is therefore safe; it only makes small text smaller to aim at, so zoom back in before drawing on anything fine.
Several short captures usually beat one tall one
Redaction is a scoping decision before it is a drawing job, and a single tall file forces a single scope. Four separate screenshots can be reviewed one look at a time, sent or withheld individually, and a mistake in one does not travel with the other three. One capture of the same material is all-or-nothing, and it quietly invites you to include everything for context, which is the opposite of sending the least that answers the question.
Keep the single tall file for cases that genuinely need it: a continuous record where gaps would look like editing, a thread whose sequence is the point, a form that takes one attachment. When you are in that case, treat the height as a workload rather than a detail — a forty-screen capture needs two complete end-to-end reviews, one before you draw and one on the exported file, and that is a different kind of task from redacting a screenshot.
A running order for a long capture
1. Ask whether you need the whole scroll. The recipient usually needs two screens, not forty. Shortening the capture removes more risk than any cover you can draw.
2. Split it at the source if you can. There is no crop and no split in this editor, so the only cheap way to make the file smaller is to capture less of it in the first place.
3. Scroll it end to end before you draw anything, at a zoom where the text is legible, and write down what you find. This pass is for finding and counting, not for covering.
4. Note the repeats explicitly. Pinned headers, sidebars, seam overlaps, and any identifier that sits in a column. These are what a single pass misses.
5. Work top to bottom in one continuous pass, and keep a landmark. Cover the last item visible in the panel before you scroll, so you always know where you resumed and never scroll past a band of rows untouched.
6. Prefer full-width bands to tight boxes. A rectangle spanning the whole image width at each occurrence of a repeated column is faster to draw, leaves no readable survivors at the edges, and its outline describes the layout rather than the length of what was underneath it.
7. Use Black Box. Blur and Pixelate take their strength from the selection’s bounding box, so a long shallow band — exactly the shape this job calls for — gets the weakest treatment either method can give.
8. Do a second end-to-end pass looking only for repeats. Not for new items: for uncovered copies of the items you already covered once.
9. Export once, then review the exported PNG at full size in your own viewer, scrolling it end to end. The editor view is downscaled; the file is not.
10. Check the file size before you send it. A tall capture is a large PNG, and what happens next is covered in when your redacted file is too big to send.
Memory, undo and a very tall canvas
This page keeps a full-canvas snapshot when the image loads and pushes another before each cover you draw, which is what makes Undo exact. A snapshot of image data holds four bytes per pixel, so the arithmetic on a long capture is unkind: a 1,080 by 12,000 canvas is about 50 MB per snapshot, and ten covers on a file that size means several hundred megabytes of snapshots held in the tab alongside the canvas itself and the retained original.
How much a given browser on a given device tolerates varies, so treat this as the mechanism to suspect rather than a fixed limit. If a long job becomes sluggish, or the tab gives out after several covers, this is why. Three practical responses: prefer fewer, larger covers to many small ones, which is the right technique on a long capture anyway; split the capture at source so each file is a fraction of the height; and remember that Clear repaints from the retained original rather than stepping back one move, so on a long job it costs you the entire pass, not the last cover.
There is no persistence of any kind here — no saved progress, no stored positions, nothing written outside the open tab. A tall capture that takes twenty minutes to work through is twenty minutes that lives entirely in one tab, which is an argument for splitting the job and for pressing Download at a sensible point rather than at the very end. Download can be used more than once in a session, and each export is written from the canvas as it stands.
On a touch device, a swipe inside the picture draws
Once an image is loaded, touch events on the image panel are taken as drawing gestures and the default behaviour is suppressed. That is right for drawing a cover with a finger and awkward for a long capture, because a swipe inside the picture does not scroll the panel — it starts a selection. Short drags are discarded silently, under four image pixels for a rectangle and six for an oval, so a quick flick usually leaves nothing behind; a long swipe, though, paints a band across content you may have wanted to keep. Undo steps back exactly, so nothing is lost, but the rhythm of scroll-check-scroll that a long capture demands is not available inside the picture.
The workable approach on a phone or tablet is to scroll the page itself, using the area outside the image, and to accept that a very tall capture is genuinely hard to review on a small screen. This is the case where doing the work on a machine with a mouse or trackpad, or splitting the capture into several ordinary screenshots, pays for itself immediately.
What the editor above does and does not do here
The tool on this page is region-based: three methods — Black Box, Blur, Pixelate — across three selection shapes, rectangle, oval and freehand lasso. Each operation replaces the pixels inside the path you drew and leaves every other pixel alone. The canvas is created at your image’s exact pixel dimensions, Download PNG writes that canvas out as a timestamped PNG, and the whole thing runs in your browser on your own machine with nothing stored anywhere.
Five limits matter for a long capture. There is no crop, split, resize or rotate, so you cannot cut a tall file into pages or trim the part you do not need — that decision belongs to the moment of capture. There is no search and no text recognition, so nothing can find the repeats for you; the sweep is manual, which is why counting instances up front does real work. There is no counter or list of covers, so the only record of what you have covered is the image in front of you, and on a file nineteen screens tall that record is only as good as your landmark discipline. Very small drags are discarded silently — under four image pixels for a rectangle, six for an oval — which is easy to hit when you aim at a thin row of text on a view scaled to 0.86, so drag a taller band than looks necessary and confirm it appeared. And covers are destructive: Undo steps back through exact snapshots while the tab is open, Clear repaints the original, and the exported PNG has no layer to switch off and nothing underneath it.
Common mistakes and misconceptions
“I covered the account name in the header.” If the header was pinned, it is in the file at every frame boundary. Count the copies before you decide you are finished.
“The editor only showed me part of it, so it only saved part of it.” The canvas is the full image and Download writes the whole canvas. The unreviewed remainder ships with the rest.
“I watched it scroll past while I captured it, so I have seen it.” You watched motion. Reading is a separate pass and it is the one that finds things.
“It is the same information repeated, so one cover is enough.” Each repetition is its own pixels. The editor has no idea that two regions say the same thing.
“I will blur the whole left column in one long band.” A long shallow band is where Blur and Pixelate are at their weakest, because strength comes from the bounding box. Use Black Box.
“Nobody scrolls to the bottom.” Recipients do, and anything that indexes or parses the image does not need to scroll at all.
“A timestamp is just a timestamp.” In a stitched capture two clocks can disagree, which dates the capture and shows how long it took.
“I will crop the bottom off here before I download.” There is no crop in this editor, and cropping elsewhere changes the frame so the export can no longer be compared with the original.
“I will pinch-zoom on my phone to check it.” Touch inside the picture draws rather than scrolls or zooms. Review a long capture somewhere you can scroll it comfortably.
“I checked it in the editor at full width.” The editor view is downscaled and clipped to a panel. Open the exported PNG at one hundred percent and scroll it end to end.