How to make a transparent background
Transparency has to be stored by the file format, and only PNG, WebP and GIF can store it — JPG cannot. If a transparent image keeps coming out with a white or black box, the cause is almost always that it was saved as JPG, or opened in software that does not render an alpha channel.
Why your transparent image has a white box
The most common cause is the export format. Saving a transparent image as JPG forces every transparent pixel to a solid colour, because JPG has no alpha channel at all. Re-export as PNG or WebP.
The second cause is the viewer. Some older desktop software renders unsupported alpha as solid black. The file is fine; the program is not. Flattening the image onto a chosen background colour before you send it removes the ambiguity.
The third is a flattened export from a design tool — a background layer left visible, or an "export with background" option left on.
Removing a background versus adding one
Cutting a subject out of a photograph is a segmentation problem and needs an AI background remover or manual masking. It is genuinely hard, especially around hair and semi-transparent edges.
The opposite — putting a known colour behind an already-transparent image — is trivial and exact, and is what most people actually need when a logo looks wrong on a dark page.
Checking that transparency survived
Open the exported file over a chequerboard or a strongly coloured background. If the corners show the colour behind, the alpha is intact. If they show white, it was flattened on export.