Make one long screenshot from many
A long screenshot is several captures of one page, each repeating a strip of the one before. Stitching is finding that strip, cutting it out once, and leaving the fixed bars where they belong. Most of the work is done before you open a single file.
Capture so there is something to match
Scroll by less than a screen each time — about two thirds is right — so every capture repeats a generous band of the last one. The detector needs that band to find where two captures meet; a capture that starts exactly where the previous one ended leaves it guessing from nothing, and a gap leaves a hole no tool can fill. Keep the zoom level the same for every capture, wait for images and adverts to finish loading before each one, and avoid anything that moves: a playing video, an animated banner or a typing indicator changes between frames and makes the shared band disagree with itself.
- Same width, every time. Captures of one page scrolled are all the same width. A capture from a different device or a rotated phone is refused by name rather than stretched to fit.
- Text and edges are the best anchors. A strip of plain background matches anywhere, so the detector scores it low; lines of text, card edges and icons match in exactly one place.
- Mind the sticky parts. A header that stays put while the page scrolls is in every capture. That is fine — it is found and handled — unless it changes as you scroll, shrinking or showing a different title.
What the detector measures
Each capture is reduced to a narrow grey profile of its rows. Bands that are identical at the top and bottom of every capture — the status bar, the app’s title bar, the keyboard, a cookie banner — are recognised as fixed furniture and set aside, up to a quarter of a capture each. Then a strip near the top of each capture is slid down the one before it and scored at every position by normalised cross-correlation. The best position is the proposed overlap; the second-best is kept too, because when two positions score almost alike — a list of identical rows, a repeating pattern — the honest answer is “check this one”, not a confident guess.
A second pass re-measures the fixed bands and each overlap at full height, which is what removes the last row or two of a navigation bar that a coarse match leaves behind. Nothing is cut until you accept: the proposals are drawn as dashed bands on the preview, each with its score.
Fixing a seam by hand
A seam the detector got wrong usually shows as a doubled line of text or a line missing. Open that seam in the Seams step, look at the full-size loupe, and drag the overlap until the text runs straight through — one pixel at a time with the arrow keys, ten with Shift. A seam you set yourself is never moved again by a later detection pass. Before you save, the Save step lists every seam in one line — matched cleanly, set by you, or worth a look — and the save button says how many uncertain seams you have not opened yet.
Covering what should not be shared
Chats, receipts and banking screens carry names, numbers and faces. The Save step has a pad where you drag across anything that should not leave with the picture; it is filled solid black when the file is drawn. Solid on purpose: a blur or a pixelation of a short number can often be reversed, and a solid box cannot.
When the result is too tall
Six phone captures make a picture well over 10,000 pixels tall, and messaging apps shrink pictures that tall until the text cannot be read. Two answers. Split for sharing saves the result as numbered parts no taller than a limit you choose — 4,096 pixels, or one phone screen — each repeating a few rows of the last so nothing falls between them. Or page it: merge images to PDF cuts a long image into pages and moves each break to a quiet row so no line is sliced in half.
Stitching works when the captures are the same width and the content sat still. It will not cope with a sticky header that changes as you scroll, a video mid-page, or captures taken at different zoom levels.