Scenery question about photo type files

First - I apologise for this question as I am inexperienced in making
scenery files for FS. I have seen scenery files (such as in Lago) in
which the object is a flat (one demensional) photo of a person which
can be placed anywhere. What kind of files are these and how does one
go about making a photo file (say of a person) to insert into FS 2004?
I am not talking about something as complicated as a building - just a
flat file of a person. Again, I am a real newbie in this area so
please forgive the ignorance of this question. And thanks for any help
you can give!