Why the result is a PNG, not a JPG
JPG is a great format for photos, but it has no way to store see-through pixels - every pixel in a JPG is fully opaque. To actually remove a background you need a format that supports transparency, which is why the cutout comes back as a PNG even though you uploaded a JPG.
Where JPG background removal is used most
- Phone and camera photos of a product, for a marketplace listing.
- A portrait or headshot for a profile picture or ID-style photo.
- A photographed object that needs to sit on a different background.
Getting a clean cutout from a JPG
JPG compression can soften fine edges slightly, especially around hair or fur, which can make the cutout a touch rougher than a source PNG would give. A photo with good, even lighting and a subject that stands out clearly from its background will still cut out cleanly.