Yes, you can do this.
Put your placeholder frames on the master page. If you leave them empty you can place images into them on your live document pages by moving your loaded curosor over them and clicking when you see the cursor shange to be enclosed in (). If you put a placeholder inage into them you will need to override them before you replace the image by holding down the Shift and Cmd (Ctrl on Windows) keys and clicking on them.
Thanks a lot, you have been so fast and usefull.
I've got another question: is there a way to do the same thing but pasting an image (a qr code) in the placeholder instead of opening one saved on the computer?
Yes. After "overriding" the frame as Peter described, choose Edit > Paste Into...