print design - Optimizing Images for Printing

I'm looking to snag some open source image from this collection on Flickr and print them on a 3in x 5in sheet in notebooks like this:

I know the resolution is much lower than it needs to be (72dpi vs 300?) but are there any strategies I can use to lessen the pixelation effect? One thing I was thinking about was making the images 50% transparent. They're just background images so I don't need them to be crystal clear.