How to make a decal following the cam

So recently , I’ve been thinking of how Decals can follows the cams. And I don’t really know how.
Here is what i’m talking about :
ROBLOX | NORNS | Full Walkthrough - YouTube

I’ve talked to the developer and he told me that was scripting.
Anyone how to do that ?

The easy solution would be to use a BillboardGUI with an ImageLabel.

The harder solution would be to point the part by using CFrames towards the HumanoidRootPart. With this method you could also only change the X, Y or Z axis of the part.