Select your image, copy it (Ctrl-C), then select the rectangle that is the center of the picture frame and Paste Inside (Edit > Paste Inside or Ctrl-Shift-V).
(Psst! Linda! You didn't type anything. )
Actually, I did type something. For some reason, when I attempt to reply by email, only the subject gets posted. Is there some setting I need to change?
Anyway, Here's what I sent:
Pasting an image into the frame image will replace the frame image with the pasted one. The best way to get the result you want is to draw a rectangle that fits inside the "hole" in the frame, and paste your image inside of that. Alternatively, just crop the image to fit inside the frame.