A mirror operation changes the placement of content without changing the image dimensions. It can be useful for a design element, but it can also reverse text, logos or a recognisable location.
Image Flip Tool offers horizontal, vertical and both axis flips. These are different from rotating a picture to make it upright.
Read each direction literally
A horizontal flip exchanges left and right. If a subject starts near the left edge, it appears near the right edge in the result.
A vertical flip exchanges top and bottom. Choosing both axes performs both reversals and is equivalent in placement to a 180 degree turn of the rectangular image.
A 400 by 300 source remains 400 by 300 in all three choices. The operation moves pixels within the same shape; it does not create a portrait canvas or a crop.
Check writing and symbols
Lettering in a horizontally mirrored photo becomes backwards. A product label or official emblem can therefore become unsuitable even if the composition looks more balanced.
For a selfie, decide whether you want the camera's familiar mirrored appearance or the orientation required by the receiving application. The tool does not decide which version is authentic or appropriate.
The same direction can be applied to a batch. That is convenient for repeated design assets, but mixed photos deserve a quick individual review because some may contain text while others do not.
Keep the original and compare a distinctive feature near one edge. That confirms the selected direction more clearly than looking only at a centred face.
If the goal is to correct a sideways image, use the rotation tool instead. Mirroring a sideways photograph changes its handedness without necessarily solving the orientation problem.