Put a white background behind a photo
The same surface, opened on the value a form means when it says plain white — with the off-white alternative one swatch along, for the upload checks that refuse a perfectly even ground.
JPG, PNG, WebP, GIF, BMP, TIFF and ICO open straight away. HEIC from an iPhone pulls a decoder the first time it meets one.
The ground, the edge and the shadow appear here once a photo is open.
Nothing is sent anywhere: the picture is read into this page and stays in it.
Which white, and why there are two of them
Nobody who asks for a white background means the wall in your hallway. They mean a ground with no detail, no gradient and no cast — a value close enough to the top of every channel that a reviewer reads it as blank paper and an automated check measures it as one number. That is what the document white swatch puts there: the same value on every pixel the selection calls ground, across the whole frame, with nothing left of whatever was behind you.
The second swatch exists because a minority of upload systems distrust exactly that. A region of perfectly uniform maximum white is also what a blank scan, a failed export or a corrupted JPEG looks like, and a handful of portals refuse it on those grounds without saying so in the rejection notice. Portal off-white sits two steps below the ceiling: it still reads as white to a person, it still satisfies the instruction, and it carries enough variation to clear the check. If your photograph was refused for its background and you know the background was white, that swatch is the first thing to try.
The halo, and what it actually is
The thing that gives away a badly swapped white ground is not the white. It is a thin ring of the old room, one to three pixels wide, following the outline of the hair and the shoulders. Those pixels are not a mistake in the selection: at the boundary, a single pixel genuinely contains both subject and wall, mixed in whatever proportion the lens and the sensor arrived at. Lay them on white untouched and the wall’s colour comes with them, which is why a person photographed in front of a green sofa ends up with a faint green outline on a white form.
The edge control that says it unmixes the old ground is what removes it. For every pixel in that partly transparent band it takes the colour it can measure, subtracts the share contributed by the wall the page sampled from the frame’s own border, and keeps what is left as the subject’s true colour. It is on by default. Turn it off on a photograph where the subject and the wall were genuinely the same colour and you will see what it was doing.
The feather control is the other half. Zero gives a hard outline that looks cut with scissors; four gives a soft one that looks like a bad selection. The default of a little under one pixel is where a portrait at ordinary phone resolution stops looking like either.
Where to go next
- Passport photo backgroundWhat each authority asks for, and the ground that satisfies it.
- White background rules for Indian formsWhat plain white means across passport, commission and bank portals.
- Why a swapped background looks fakeFour giveaways, each with the control that fixes it.
- Change the backgroundOpen a photo, select the subject, put a new ground behind it.
The image you open is read by this page and by nothing else — there is no server behind this domain that could receive it, and the outline is worked out by arithmetic running inside your own browser rather than by something your photo is handed to.