Front cameras mirror what they capture, which is why selfies often look subtly wrong and any writing in them appears backwards.
A horizontal flip mirrors left and right; use it when writing in a saved selfie appears backwards. A vertical flip mirrors top and bottom. A genuinely upside-down photo usually needs a 180-degree rotation, not a vertical mirror.
Illustrative example: compare a readable shirt logo in the original scene with the saved selfie. Flip horizontally once only if it was mirrored; check the exported image rather than assuming every front-camera photo needs correction.
The image is exported from a canvas. JPG and WebP are re-encoded and can change detail; this is not a byte-for-byte lossless transformation. Keep the original and inspect fine text in the result.
Flip across mirrors the picture from left to right, which is what you want for a selfie that came out reversed. Flip down mirrors it from top to bottom. Neither one is the same as a half turn, which keeps the picture the same way round but upside down.
Be careful with any picture that has writing on it. A flipped sign reads backwards, so flip it again to restore it. Flipping only moves the pixels, so nothing is lost, although saving a JPG encodes it once more.
Not for JPG or WebP exports, which are encoded again.
Use quarter-turn rotation rather than a flip. A flip mirrors the content.
Flipping mirrors the picture, so writing reads backwards. Turning rotates it, so everything stays readable but at a different angle.