JPEG, PNG, and WebP for uploads
Which format survives a size cap, and which one a form will refuse.
JPEG throws away detail the eye barely uses, so photographs get small. PNG keeps every pixel and is the right choice for a diagram with flat colors and text. WebP can do either job. A form that lists “JPG only” will still refuse a WebP, even when the WebP is smaller.
Use JPEG for a face, a scanned page that is mostly photo, or any preset with a kilobyte ceiling. Use PNG when the page must stay sharp and the cap is generous. Use WebP only when the portal names it.
On Resize, pick the format before you download. If the browser cannot encode WebP, the tool falls back to JPEG and says so in the status line. Nothing is uploaded while you try.
Do not rename a PNG to .jpg. The extension and the bytes have to match. Photo check accepts JPEG only. The browser checks the real type when it can decode the image.