Originally Posted by Quint
If you do desire a border it can be made simply. I use Photoshop Elements. After opening the image I go to the "Image" tab in the upper left then "resize", then choose "canvas size" and put in your desired widths and color.
You can do this in Gimp also. (A free app.)
I would put the borders on there then the buyer can choose how to frame it, with a border showing or without. The border also helps protect the corners of the actual printed area. If a corner gets damaged you can still frame it with a mat covering the border.