Is the photo uploaded?
No. The model file is downloaded into your browser and runs there, and the photo is decoded on a canvas on your device. Nothing is sent to a server, so there is nothing stored and nothing to delete.
Why did the edge come out rough on a big photo?
The segmentation model works at a fixed 320 × 320 and its mask is stretched back up to your image, so the larger the photo the further each mask pixel has to travel. Measured on the same subject, boundary accuracy fell from 0.81 at 0.2 MP to 0.42 at 14 MP. Feeding it a 1–2 MP copy usually gives a crisper sticker than a 12 MP original.
Can I fix a bad cut-out here?
Not in this tool. It runs the cut-out and draws the outline around it. When a subject needs hand correction, take it to Background Eraser, which has the magic wand, the erase and restore brushes and per-stroke undo for exactly that job, then bring the transparent PNG back here: an upload that already carries its own cutout is outlined as-is, with no model run.
Will this give me a cut line for a vinyl cutter?
No. The output is a PNG image with a transparent background and a painted border, not a vector cut path. A cutting machine needs a real path. The Image Vectorizer traces a silhouette and exports it as SVG, DXF or G-code, which is what a machine can follow.