u can use ms paint to trace around the main image in a clear color or same color of focal point and do a background fill. Or cut out pic and paste on bg you want. Save an extra copy and only work with one in case u mess up. Hope this helps.
Paint Shop Pro and Adobe Photoshop make it easy. Problem is, they are both expensive s/w packages. You really have to have a compelling reason to fork over that much money.
