Change a photo background to light grey or white

The background is the requirement people treat as cosmetic. It is not: several consulates reject photos specifically because the background colour suggests the wrong template, and the fix is easier than reshooting — provided you understand which colour is wanted.

Which colour, for which document

Pure white or off-white — United States, Korea, China, Japan, India. Straightforward, and the most common requirement worldwide.
Light grey — Schengen consulates, and the UK (which also accepts cream). A white background is the most frequently cited rejection reason for Schengen applications.
Light grey or white — Canada, Australia, Germany and France accept either, with some preference for grey.
Blue or red — used for domestic documents and exam registrations in China, not for visas. Follow the notice for the specific registration.

The practical upshot: if you are preparing one set of photos for both a US application and a Schengen one, they cannot be the same image. Prepare them separately.

Why not just reshoot against the right wall?

You often should, but it is not always practical. Reasons people end up fixing the background instead:

The photo itself is good — the expression, the framing, the lighting — and only the wall is wrong.
The nearest suitable wall is a colour you cannot change, or the room is too small to avoid shadows.
The original was taken elsewhere and cannot be repeated.

How background replacement actually works

There are two approaches, and the right one depends on the photo.

Flood fill from the edges. The tool samples the border pixels, works inward, and replaces connected areas of similar colour. It is fast and produces crisp edges on hair-free outlines. It struggles when the background has a gradient, or when the person's clothing is close in colour to the wall — which is why wearing a dark top against a light wall is such good advice.

Chroma-key or model-based matting. More robust on difficult hair, but heavier and usually server-side. If a site offers it for free, ask what happens to your uploaded photo.

For a passport-style photo against a plain wall, flood fill is usually the better trade: it is deterministic, you can see exactly what it did, and it runs in your browser.

Doing it without uploading

Open the background removal tool.
Choose Automatic — it samples the four edges of the image. If the result is patchy, switch to Manual and click the wall colour directly.
Set the fill to Pure white for a US, Korean or Chinese application, or use a custom light grey for Schengen and the UK. Around #f2f2f2 works well for grey.
Raise or lower the tolerance if the edges are eating into your hair or leaving a halo.
Download the PNG, then compress it to the required file size.

The whole operation happens on your device. That matters more here than anywhere else: a passport photo is exactly the kind of file that should not be sitting on a stranger's server, and most free online background removers upload it.

Then check the head ratio

A correct background does not help if the head occupies 40% of the frame. After the background fix, crop to the document's required proportions — see the head ratio guide, or generate the finished file directly with the ID photo tool, which handles background, crop and file size together.