attaching postcards to unfinished wood

[frecklestars.livejournal.com]

I have postcards that I'd like to attach to some unfinished wood beams (they're about 100 years old, not splintery or anything, but definitely an uneven surface) in my apartment. However, because I like to complicate things, I don't want to use pushpins or put holes in the postcards. That said, how would you go about attaching the postcards to the wood (non permanently)? I'm thinking some sort of tape, but I don't want to go experimenting, especially if someone has an idea.

x-posted to saucyhelp, hopefully you didn't have to read this twice