when are the satellite images updated?

Answer 1

Satellites are continually taking images so they are frequently updated. Now if you are talking about the background images for a particular vendor (i.e. Google Maps, Yahoo Maps, etc...), you will need to check their policies on purchasing data access. If you have a specific site, please post as additional information.

If you are looking to purchase commercial imagery, why not check out http://www.geoeye.com/ or http://www.digitalglobe.com/.