This tool is useful for would be architectural photographers, but may help anyone out who has an image that looks a bit unatural due to a low viewpoint (it happens a lot). Gimphoto has a specific tool to correct it quite easily.
For this task, we'll use the picture of the Council house in Nottingham.
With the Council House image open, one really useful tip is to zoom out of the image to leave some area around it. This will make it easier to see if your correction is OK.
Step 2 - Select the Perpective tool 
With the image open, select the Perspective Correction tool, highlighted by the red box on the left.
Ensure that the whole image is selected by using the menu option: SELECT > SELECT ALL
Then click and hold on a corner point of the image. The Persepctive dialogue will appear (move it so that it overlaps the ruler a little) and you can hold and drag the top right corner point of the image to 'distort' it.
Look at the verticals of the columns. Make them align to the vertical 'edge' of the image.
To complete the image, adjust the left hand corner as well. When you are satisfied with the result, you can crop the image. This is done by ticking the 'Crop to result' box in the Tool Options part of the Tools palette (see right) and then using the 'Transform' button in the Perspective dialogue box (see left).
Again, use FILE > SAVE AS to save your edited image as a new file.