VIews with Images problem

I seem to have come across a problem with using views to grab a random image and post it in a block. The site cn be seen at:
http://mdg.loesje.org/admin/build/block
you'll note the large poster image on the right most collumn which is a block view:

• Fields: Image: Display Image, option; preview
• Filter: Node: Type: 'is one of': 'Image;
• Filter: Taxonomy: Terms for Image Galleries: 'si all of': 'E-Cards'
  and thats about it

Works exactly as I want it except that every time someone views a page with it it generates another 'preview' image, which chewed up all the server space after a few weeks. Is this a bug with views or with the image module?