I was exploring the Amazon print service Createspace and for that, your covers need to be at least 300dpi. Considering that I designed all of my covers for Kindle and the web, I worked in the web standard 72dpi, which is significantly smaller. Since you can’t just scale the image larger without ruining it, I had to see if I could rebuild it from scratch at 300dpi. Turns out it’s not that hard.
I’m not actually making any real plans to publish print copies any time soon. I might when a particular book is finished, but at this point I don’t know how long that will take. Either way, it won’t be for quite a while. I’d like to make them comic book sized though. I think that would look pretty awesome on a shelf.