In compass v0.11 you can watch arbitrary files and react to them yourself. Just add one or more watch commands to your configuration file:

compass.rb

watch "images/*" do |base, relative|
  puts "File size of #{relative} is: #{File.size(File.join(base, relative))}"
end

output.txt

>>> Compass is polling for changes. Press Ctrl-C to Stop.
>>> Change detected to: images/border.png
File size of images/border.png is: 3712