Mirror a picture left to right, top to bottom, or both at once — the selfie that came out the wrong way round, or a texture that has to tile. The dimensions and the format stay as they were; only the pixel order changes.
Both boxes together is the same picture as a 180° rotation. For 90° turns, use the Image Rotator.
The edit is redrawn on a canvas in this tab and re-encoded in the format you dropped — JPEG stays JPEG, PNG stays PNG, and anything else comes back as PNG. Nothing is uploaded.