The hugin panorama creator is a great tool for photographers who use Linux. It has great abilities to merge photos into a nice panorama image. Hugin,  The Panorama photo stitcher is absolutely great. I just tried it with two photos I took some time ago and jumped on my terrace to make a series of 6 I could merge to a single image. It worked outstandingly.

hugin screenshot

This shows how you can connect the different images with points where the same object or same pattern appears. (I know these images are horrible, I should have taken 2-3 more of that building. Btw, this is the town hall of Flensburg.

The hugin website offers a lot of tutorials which I definetly going to have a look at.Puzzling images together in GIMP can really consume a lot of time. *sigh*

Here my first results:

rathaus flensburg panorama_clipped