Create a user friendly workflow to create banners
The simplest would be a content type with an image field and a text field. The image field would be the banner and the text field would be the path on your website where it should be displayed.

Create a view that filters on that content type and has the image as the field it displays.  Put the path field as an argument.  Configure it to return only 1 item.

In a block, call that view using $_GET['q'] as the argument. 

Image is displayed in the block.  Display this block on your page where you want your banner.

Don't like blocks?  Put this in a page_preprocess() hook and assign the view output to a variable and put this in your page where ever you want it.

Get fancy?  Randomize the sort so if more than one of these content types has the same path a different image is displayed on each page load/reload.

Get fancier.  Use the views_nivo_slider module ( http://drupal.org/project/views_nivo_slider )