How to make images transparent?

I have a rough storyboard layer that are all imported jpg images. I want to fade them down so I can sketch drawings on top. Just like if I was to reduce the opacity of a layer in After Effects.

Maybe replace these images with an updated set that is faded, (aka ghosted) or has transparency? Although that seems overly complicated way to go about it.

Toon Boom Animate 3 user since January 2014
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Thanks, I tried that before and it wasn’t working but I tried again after seeing your video and it works fine. I must have been too tired.