seperating directories from files

[raj]

i'm surely a newbie in python and on the go, I just tried to write a
small app to change the gnome desktop background daily. It's working
now making use of listdir() to find the contents of each dir I
encounter. But I'm sure that my code won't go that smooth forever.

How can I find if the content is a Directory or not and if it's a file,
whether it is an image file or not?
Is there any method to read the metadata of files?
Thanking all of you in advance.....