Confused about ImageCropper plugin's capabilities

I've successfully installed ImageCropper, and I created a couple of prototypes. Next I cut and pasted the example seen here: http://www.endevver.com/plugins/image-cropper/documentation/, i.e,

<mt:Asset id="136">

  <mt:CroppedAsset label="Square">

    <img src="<$mt:AssetURL$>" />

  </mt:CroppedAsset>

</mt:Asset>

but I get -- nothing! Is there some other step I'm supposed to do? The documentation is ambiguous IMHO as to whether the plugin does the actual cropping or it merely fetches a pre-cropped image. I've tried both but I get no result either way. Interestingly, when I tried the other code example on the ImageCropper i.e.,

  <mt:CroppedAsset label="Square">

    <img src="<$mt:AssetURL$>" width="100" height="100" />

  <mt:Else>

    <img src="<$mt:AssetThumbnailURL square="1" width="100"$>" />

  </mt:CroppedAsset>

It defaults to the "Else" logic every time. (a single instance, wrapped in an mt:Entries loop, etc. )

So I guess I'm asking whether this plugin crops on the fly and whether anyone has some actual working code utilizing it I can look at.

Thanks!