How do I attach something to old wood without damage?

I inherited an old Hall Tree from my grandmother's house. The mirror had been broken so it just has a big empty space. I thought I might just cut cardboard to fit and use wrapping paper as decoration instead of trying to replace the glass. Is it safe to just use duct tape to hold in place? I don't want to ruin the finish on the wood even if it would be on the back where no one would see it.

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