Well I would say that you could do it with a paint package but a stamp based mapping app is better. I write ViewingDale which would be ideal for this. There is DungeonForge and Dundjinni too as both are well set up for this kind of thing too and I would have thought that FM8 would have been capable too. Still, if you say that DungeonForge and FM8 are off the list then try mine and Dundjinni and see how you get on. Theres a free limited demo on ViewingDale on the web site. Not sure if Dundjinni is doing demos. In a similar vein some of the VTTs can do the same kind of thing so you can add BattlegroundsRPG and MapTool to the list as well. There was a chap Toga Mario doing something like this too but cant remember what his app is or was called but his name is pretty unique to get into a search engine.

If you want a video demo of mine then shout.