A few nice online image editor images I found:
Halloween volunteers - The Lomo Gang
Image by zenera
Created using pxn8.com, the online image editor - Princeton and Leafy ready for Halloween
with some human presence in black and white
Image by jorgempf
done from this image:
www.flickr.com/photos/jorgempf/1449771262/
using this online image editor:
www.myimager.com
sugested by Tiago Salgado
operations:
1. sarpen level 3
2. grayscale
inspired in this comment from mgbon:
have you tryed black and white?