There are a number of programs for "stitching" together a series of overlapping photos to create a panorama.
I have tried a few but most are not very intuitive to use and some don't do a very good job.
The best by far of those I have found is a free one from Microsoft. You just drag and drop overlapping photos from your hard drive into its window and within seconds you are presented with a perfect panorama.
Download from here...
http://research.microsoft.com/en-us/um/redmond/groups/ivm/ICE/PS
I have also used it successfully to produce a composite map from scans of 4 pages. However - the individual images to be merged must overlap for the program to sense how they are to be combined. It will not automatically butt together images without an overlap.