Photos are harder at the edges than flat graphics
A logo is usually a clean shape. A photo has hair, fur, glasses, soft shadows, and backgrounds that share colors with the subject. The model estimates that boundary. A plain wall or studio sweep is easier than a subject standing in front of a detailed street.
Preview the cutout against the checkerboard. Look at hair, ears, fingers, and the gap between an object and its shadow. If a piece of background remains, or a piece of the subject is missing, try a photo where the subject is more clearly separated from the scene.
Portraits and product photos
Portraits are a common reason to remove a background: a new backdrop, a profile picture, or a layout that needs the person without the room. Product photos are another: the item needs to sit on white or on a store template. Practical notes for catalog images are in how to remove a background from a product photo.
Phone pictures work the same way as desktop files. The phone guide covers choosing a photo from the camera roll and saving the PNG.
The photo is processed locally
The picture you select is processed on your device. It is not uploaded for background removal. Very large photos, over 15 MB or 24 megapixels, are declined. Photos that are accepted but still very wide are scaled down before processing, and the download matches that size.