About using Photomerge

You can use the Photomerge command to combine several photographs into one continuous image. For example, you can take five overlapping photographs of a city skyline, and then assemble them into a panorama. The Photomerge command is capable of assembling photos that are tiled horizontally as well as vertically.

Transforming and Retouching > Creating panoramic images using Photomerge > About using Photomerge