[Scribus] newbie question: picture size

[D. R. Evans]

I apologise for the simple question. I have looked in all the dialogs
and menus and can't see how to do what I want :-(

I have created an empty document, and created a frame for a picture.

The picture exists as a PNG file, intended to be printed at 300dpi.

But when I "Get Picture", only part of the picture fits in the frame.
And if I click "Info" on the picture frame, it says that the original
DPI is 72 and the Actual DPI is also 72.

Where does Scribus get the number "72" from? and how do I change it so
it knows that I am working at 300dpi?

(This is 64-bit Scribus 1.2.4.1, as supplied with Kubuntu dapper.)