JPG is the safest default for photos
JPG is widely accepted, compresses photographs efficiently, and usually reaches tight KB limits more easily than PNG. It does not support transparent backgrounds.
PNG is useful for graphics and transparency
PNG keeps sharp edges and transparent pixels, which suits logos and screenshots. Photographs saved as PNG are often much larger.
WebP is compact but not universal
WebP often produces a smaller file at good quality. Use it only when the upload instructions explicitly include WebP; older portals may accept JPG and PNG only.