Get original image format and msoPicture Export command

[Daniel Kirsch]

1.
Is there a way to get the original format of an image?
I export a msoPicture shape using its Export command. Usual "jpg" gives
me the best file size, but for semi transparent images I would like to
use gif. Probably the easiest way would be to just get the original
format and use that or something like:

if (origFormat == "gif")
useGif
else if (origFormat == "png")
usePng
else
useJpg

2.
Is there some documentation about a shape's "Export" method? I just have
found an example and some hints but no real documentation.

Thanks
Daniel