Rotating and Flipping Your Photo
If you rotate your camera sideways to take a picture, you might need to rotate the resulting image too. The easiest way to do this is to click the Image menu, and then use the rotation options in the Transform submenu there. You can rotate clockwise or anticlockwise by 90 degrees, rotate the image by 180 degrees, and flip it horizontally or vertically.
If you have a photo that’s slightly wonky, you can manually adjust it in GIMP. Click the Rotate tool (or use Shift+R) and you can enter an angle for rotation, or click and drag the image to rotate it. To change the pivot point about which the picture rotates, click the circle in the middle of the image and drag it.