aak sarmad glad to see you back...
hope you are doing well...
I am currently working on another photoreal project at the same time.
It depends on what you really want.
If you want the terrain to have accurate land elevations such as hills, coastlines, high ground, low ground, then you can need a good source of raw geographic data that consists of numbers. FSX provides terrain gamepacks where you can convert those numbers to usable FS files.
FS9 is bit simpler, you can use Sbuilder9 to do conversion, but I think when it comes to elevation, you can use your FSX result files in fs9 as well.
Second Sbuilder9 for FS9 and SbuilderX for FSX and bit of practise you gained from ur experience with elevation you need satellite image files which you can get from www.ptsim.com
SITE via google or yahoo earth for freeware files. For payware you may have to order seperately.
NOTE: The freeware images i researched on had google and similar tags on them.
Best place to start is to go through youtube video guide on SbuilderX.
hope this helps