OpenRaster files are ZIP archives like OpenDocument Format and even uses the same path for the thumbnail! So the allready existing ODF plug-in should be able to handle this if only the correct mime-type is added. Complete specs here: http://create.freedesktop.org/wiki/OpenRaster I've attached a file produced by MyPaint.
Created attachment 2757 OpenRaster file produced by MyPaint
Created attachment 3144 Patch that solves this issue Also applies to 0.4.1.
Moving this to tumbler which we use instead of thunar-thumbnailers these days. @Jon: We're currently finishing an ODF thumbnailer and I'll make sure to have it support the raster MIME type(s).
Pushed to the master branch of tumbler: commit 851a149213c2b3cf2c961e77cc29f18f687d409b Author: Jannis Pohlmann <jannis@xfce.org> Date: Wed Nov 2 23:13:27 2011 +0100 Add support for OpenRaster images in the ODF thumbnailer (bug #6108).