Well I've been thinking about all my circular towers and I am delighted to report that after playing around in GIMP for a while I have found a new trick!

See these images: the top one is just a photo of a stone wall I've cut into four slices and pasted roughly in a line. I didn't bother fixing the seams. This long line of wall is on a layer which is exactly the width of the image, and about four times as tall as the image, and the image is centred on the layer (changing these parameters makes a huge difference). I then select FILTER>DISTORT>POLAR COORDINATE and press OK without checking any of the settings and I get the circular bottom image. Useful!

Click image for larger version. 

Name:	Stone wall.JPG 
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