[Typo3] change page graphic dynamically

[Jane Larsen]

I want to change som of my page graphics dynamically (language
versionized in some cases):

I can make a marker in my template for it, but how do I proceed:

Lets say that the image to be placed is located in the left column of
current page, then how do I "import" it?

and just as important: how do I make a default image appear if there
is no content in that location?

//Jane Larsen