What counts as an image here
If the file is a JPG, PNG, or WebP under 15 MB and 24 megapixels, you can open it in the tool. That includes camera photos, screenshots, exported graphics, and scans saved as one of those formats. Other file types are declined so the browser is not asked to decode something it cannot handle reliably.
A photograph and a flat graphic are both images, but they behave differently at the edges. Photos are covered on the photo background remover page. Logos and simple marks are covered in how to remove a background from a logo.
Why the download is a PNG
The point of removing a background is to keep the subject without a backdrop. JPG cannot store a transparent pixel, so the result is a PNG. WebP can store transparency, but CutMyBG always downloads a PNG so the file opens predictably in design tools, shops, and document apps.
The differences between the three formats are spelled out in JPG, PNG, and WebP background removal.
The image stays on this device
The file is decoded and processed in your browser. It is not sent to a CutMyBG server for the cutout. The first run can download the AI model into the browser. That download is the model, not your image.