Retouching and restoring images : Flipping and mirroring images
 
Flipping and mirroring images
You can flip or mirror an image so that the left side becomes the right side or the top becomes the bottom. When you choose Flip, layers or selections are flipped in position. When you choose Mirror, layers or selections are flipped along their horizontal (left to right) or vertical (top to bottom) axis.
To flip a selection, layer, or image
Edit tab 
Click Image > Flip, and choose one of the following:
Flip Horizontal — the left side switches to the right side
Flip Vertical — the top switches to the bottom
Flipping a selection converts it into a floating selection, leaving the original layer unchanged.
To mirror a selection or layer
Click Image > Mirror, and choose one of the following:
Mirror Horizontal — flips the selection or layer along the horizontal axis (left to right)
Mirror Vertical — flips the selection or layer along the vertical axis (top to bottom)