Fran - The important things for me when considering a photo background, is... 

For ground base images anything with a level horizon - thats a must.
Aerial shots then any angle is OK 

Prefrably no people if possible. 

Size isn't a issue, (apart from what you can squeeze into the zip file)  I usually resample down

Does this help ?

Pinky - you left the lens cap of your mind on again.