What a vertical flip does
A vertical flip swaps top and bottom, like a reflection in a lake. Left stays left and right stays right. Designers use it to create reflection effects under products and logos, and it corrects images from some scanners, microscopes, cameras and older software that save pictures upside-down and mirrored.
What happens when you flip
Every column of pixels is reversed from top to bottom. The picture keeps its size, nothing is cropped, and no detail is lost in the flip. The result is saved as a PNG without the original camera metadata. Several pictures can be flipped together.
Vertical flip or 180° rotation?
A 180° rotation turns the picture upside down and also swaps left and right, so text stays readable when you turn your head. A vertical flip only swaps top and bottom, so text becomes upside-down mirror writing. If a photo is simply upside down, use Rotate Image 180° instead.
Common problems and how to fix them
Text reads backwards and upside down: you needed a 180° rotation — undo by flipping again. You want a reflection under an object: flip a copy, place it below the original in an editor, and fade it out. The file is large: compress the PNG afterwards.
Good habits
Decide between flip and rotate before editing, keep the original, and check text in the picture after flipping.