Ok I take back my original statement then. You could do this with the built-in categories by simply looking at the categories assigned to the document. If the user is in a specific part of the site and the document has that category assigned to it, display one image. If they are in another part of the site and that same document has the other category assigned to it, display a different image.
You can use something like this to get the categories: (I'm comparing the category name to the document name in this instance)
{%"DocumentID IN (SELECT DocumentID from CMS_DocumentCategory inner join CMS_Category on CMS_DocumentCategory.CategoryID = CMS_Category.CategoryID where (CategoryDisplayName = '" + CurrentDocument.DocumentName + "' OR CategoryDisplayName = 'All'))"|(handlesqlinjection)false@%}