Go to images.google.com and search some category of image that you want. Get the highest resolution you can find. Go to https://rasterbator.net/# and adjust your picture to what you want. You download that as a PDF file and print it with a color printer.

That's not free, but it's cheap and the result is spectacular. If you want a preview, search google images for "rasterbation". I know it sounds smutty, but that's what it's called.