Hi Burr, as far as I know IGES and STEP do not have any standard mechanism in them to hold embedded thumbnail images.

It is on my "todo" list to write a thumbnail for 3DM, but I don't expect to get that done for v2 though, it will need to wait until a future version.

There is more involved than just writing the thumbnail data itself, I also need to write a Windows shell extension that handles extracting the thumbnail and handing it off to the shell so it can be displayed by Windows. Setting that up and dealing with installing it are part of the work involved.

- Michael