Rotations and Flips

To access the editing tools, open an image and then click the Edit File toolbar button (the palette icon).

Several tools are provided to manipulate the orientation of images.

Mirror: This flips the image horizontally. The left and right sides are swapped.
Flip: This flips the image vertically. The top and bottom are swapped.
Rotate Right: This rotates the image clockwise.
Rotate Left: This rotates the image counter-clockwise.

The rotations offered in the edit mode act on the image in memory. They are not direct file operations. For jpeg images, these means they are not lossless operations - the image will degrade slightly when it it is re-encoded and saved. However, gThumb does provide lossless rotation tools. See Rotating Images Losslessly.