ImageKill removes images that match certain size criteria.
The idea is that many advertisement banners have a certain
width/height ratio by which they can be recognized. This makes
it possible to remove ads which don't give themselves away by
their name.

The filter works by examining the source URL for the image,
looking for "width" and "height" attributes. This means that
loading an image can only be avoided if its source URL
contains those attributes (which is often the case). The
advantage on the other hand is that we don't have to load the
image just to find out its size.

To avoid removing navigation bars and other images that you do
want to see, even if they match the evil width/height ratio,
ImageKill can prevent images from being removed in two cases:

* The image source tag contains a specified string/regexp;

* The source tag contains the "usemap" attribute, i. e. it's
  an image map.

Instead of completely removing the offending images, you can
also specify an URL to use as a replacement. I use a simple,
1x1 pixel blue gif image for this purpose (Netscape scales
this to the size given in the width/height attributes). This
way, the page layout stays the same; good for those pages that
rely on the geometry of their images for layout purposes.

This filter has the following configurable preferences:

* ImageKill.minheight

  Only remove images which are at least n pixels high.

* ImageKill.minwidth

  Only remove images which are at least n pixels wide.

* ImageKill.ratio

  Remove images which are more than n times as wide as they are
  high (in addition, they must match the minimum sizes given
  above).

* ImageKill.exclude

  Don't remove images that match the given string/regexp.

* ImageKill.keepmaps

  Don't remove images that contain the "usemap" attribute in
  their source URL (image maps).

* ImageKill.rmSizes

  A list of fixed sizes; you can use this instead of (or in
  addition to) the w/h ratio based removal of images: just
  specify some geometries commonly used for ads, like 468x60.
  Note that the format is somewhat rigid (comma separated
  list, no spaces allowed, geometries must be in the format
  WidthxHeight).

* ImageKill.replace

  This toggles the way offending images are handled: normally,
  they are completely removed, but if ImageKill.replace is
  true, they are replace with the given URL instead.

* ImageKill.replaceURL

  The replacement URL that is used if ImageKill.replace is
  set. Use your favorite "Ad removed!" image, or just an empty
  1x1 gif.
