JPG for photographic content
JPG uses lossy compression and is widely accepted by forms. It usually reaches small limits efficiently for photos, but it does not support transparency. Transparent areas are flattened onto a solid background during conversion.
PNG for transparency and edges
PNG is lossless and keeps an alpha channel. Logos, interface captures and line art often suit PNG, while detailed photos can produce much larger files. Very low byte ceilings may require reduced dimensions.
WebP as a modern option
WebP supports both photographic compression and transparency. It can be an efficient choice, but the receiving form must list WebP as accepted. Keep the original format when compatibility is uncertain.