I'm going slightly off-topic here but please make sure that you have the right to use the pictures if the PDF is not just for personal use.
If you're creating something for other people to see you will need to make sure that the content - including all images - is legally available for you to manipulate and then publish to your intended audience.
Not every picture on the web - including those on some, supposedly, royalty-free photo sites - can be legally downloaded or copied without the permission of the owner(s) of the photo. (I'm making an assumption here that you haven't taken the photos of the celebrities yourself since they're all kinds of sizes.)
This might not be an issue for you but I thought it might be worth mentioning as a general warning to Scribus users who are thinking of doing a similar thing.
The bottom line: Unless you know for certain that you can use a photo in your creations it's safer - and potentially much less costly - simply not to use it.
This might sound a bit "over the top" but you're better safe than sorry. However, it's your decision.
P.S. If you're using a Mac you might want to try using "ThumbsUp"
http://www.devontechnologies.com/products/freeware.html to create your thumbnails. It's free and very easy to use; just drag and drop. Or there's "Thumbscrew"
https://www.macupdate.com/app/mac/16312/thumbscrew/ which is also free and produces good results.