Pen and paper is great but if it's something I want to hold on to, I have to add it to my digital system. Sometimes that means taking my written notes, doing some editing, then saving digitally. Other times it just means taking a snapshot and saving that.

I still use Evernote for my long term storage (although I do worry about the long term viability of the company) and it does a pretty great job of finding and indexing text (even handwritten text) in images. The search operators are also pretty great.