ICO is the icon format used for favicons and Windows icons. One ICO file can hold several sizes of the same picture, from 16 by 16 pixels up to 256 by 256. Converting ICO to JPG gives you smaller files that every app, website and device accepts.
JPG is the most widely supported photo format, and it compresses photographs very well, so files stay small and open anywhere. JPG is lossy, so it discards fine detail to save space, and sharp text or line art can pick up faint blur. It also has no transparency. Converting an ICO gives you one regular image, taken from the icon, usually its largest size. Icons are small, so the result is small too, and enlarging it will look soft.
Choose High for a good balance, Max for the least visible loss, or Low when file size matters most. The pixel dimensions follow the original, each file keeps its name with only the extension swapped, and no metadata or watermark is added. Everything runs in your browser, so your images are never uploaded.
Tip: To get a usable picture of a favicon or app icon, PNG is the best choice because it keeps the transparency and every pixel exactly.
Slightly. JPG is a lossy format, so some fine detail is discarded. At High quality the difference is hard to see in photographs. Text and sharp line art show it more easily.
Icons usually have transparent corners or backgrounds. PNG and WebP keep them. JPG cannot, so transparent areas become white.
The image is read by your browser, which normally gives the largest size stored in the file.
Yes. Add them all, convert once and download a single ZIP. Only the extension changes. A file named favicon.ico becomes favicon.jpg.
No. The conversion happens in your browser and the files never leave your device.