light behind object or text

I feel crazy. I have seen this before and watched videos on it. Now that I am ready to make this happen, I can not seem to find the instructional text/video.

My goal: Have an object, like a photo, stand out in a 3-D plan with a light source well behind it. The light source is stationary, the photo moves, which causes the light to burst around it from behind.

I recall watching this and filing it in my pea brain so I could do this for a project.

And now I can not find the instructional text and have tried and tried to find out how to do this.

Thanks for any tips you can provide.