To make a background images more useful to a designer they can be made into a perfect tile. In other words a seamless tessellating image which can be repeated without any visible join. To start with select a full frame image. For this example I am using my best selling Egypt picture. The next step is to adjust the image to get it as square as possible. Photoshop's lens correction feature is very good at this as Angle, Pin/Barrel, Vertical and Horizontal Perspective can all be tweaked simultaneously with a real time preview of the image on a grid. Once this is done crop the image in a place which it will naturally tessellate.

In order to work on the edges of the image it must first be split in to four and the opposite corners swapped. This process must be pixel perfect for the final image to be seamless. I do this by cutting and pasting as well as changing the paper size so the pasted image goes exactly where it is needed. Photoshop will paste into the center of the visible paper so as long as you can see the whole page you can paste the right side on the left by doubling the paper width before you paste. This takes a while do to get all the bits in the right place. If you know a better way let me know. Now the edges that need to be worked on should form a cross in the middle of the image. To blend them together I use the clone brush in Coral Photo Paint although I'm sure other bitmap editing software has similar tools. Once all the edges are blended together swap the corners back and you have your perfect tile.