Background Remover
Drop a picture in and the background goes, leaving a transparent PNG. It works by colour, so you get a tolerance slider, soft edges, and brushes to correct anything it takes too much or too little of. Your file never leaves this tab.
Reading happens on your machine. Nothing is being sent anywhere.
Click the picture with Pick background to add a colour. Click a swatch to drop it.
How different a pixel may be from the background colour and still count as background.
Edge fixes
Pulls the leftover background colour out of half transparent edge pixels. This is what removes a green or white halo.
The selection works in CIE L*a*b*, where the distance between two colours matches how different they look, so tolerance follows what your eye calls a similar colour rather than what the RGB numbers happen to say. From the edges floods inward from the border, which keeps a colour that also appears inside the subject; Everywhere selects every matching pixel in the picture. Edge pixels are unmixed by assuming they are a blend of the subject and the background colour, and solving for the subject. This is colour based selection, not object recognition. A subject that shares its colours with the backdrop, or fine hair against a busy scene, is beyond what any tolerance slider can do; that needs a trained model, which would mean loading megabytes of someone else's code into your browser, and this site does not load anything from anywhere else.