I am missing the functionality to choose the transparency of images that were inserted by "Insert -> Image -> From File...". I think the best place for this would be the dialog where all other image properies can be changed (see attachment).
Created attachment 95591 [details]
A screenshot of the format image dialog.
I agree with you.
From my point of view this issue is very closely related to bug 75769 and therefore I mark it as a duplicate of bug 75769.
Regarding your specific question. The transparency feature you can find in the toolbar at the bottom if you click on the inserted image. Assure that you have enabled the PICTURE toolbar (-> VIEW -> TOOLBARS -> PICTURE).
*** This bug has been marked as a duplicate of bug 75769 ***
(In reply to comment #2)
> Regarding your specific question. The transparency feature you can find in
> the toolbar at the bottom if you click on the inserted image. Assure that
> you have enabled the PICTURE toolbar (-> VIEW -> TOOLBARS -> PICTURE).
THX, that's what i searched for.
So I have to change my critique from "missing feature" to that it is hidden / not intuitively to find.