Hi Stephane,
it's a serialized Gdk.Pixbuf. use gdk_pixdata_deserialize to unserialize it and save it as a png.
Thanks for that hint. It seems there would be an offical extension for PHP to handle GTK, but it crashes my webserver. Bad :-)
Just for interest - why is a pixbuf used instead of a "common" image format for this? Is it easier to handle within mono & gtk?
Cheers, Andreas