For the moment, it works with "Sprite" plugin, or plugin with a textured image. Things using internally a canvas don't work (for example R0j0hound's Canvas). I can add that, but it's going to be per-plugin specific.
.capx : http://dl.dropbox.com/u/1412774/ExtractImage/ExtractImage1.capx
Demo : http://dl.dropbox.com/u/1412774/ExtractImage/index.html
Behavior : http://dl.dropbox.com/u/1412774/ExtractImage/pode_extractImage.0.1.zip
Edit : you can pair it with http://www.scirra.com/forum/topic50604_post318757.html