Verify decal ID via script

So this has been used in many places, but I have no idea how it works.

Basically, a user inputs a number (A.K.A. the decal ID) and I need the script to verify that the decal ID is valid and is registered and working etc...

How can I do this? Thanks!

You can thank an epic update that brought the MarketPlace service for this. Here is an example script:

local ID = game:GetService("MarketPlaceService"):GetProductInfo(9001,"AssetTypeId")
if ID == 13 then
	print("Item 9001 is a Decal")
end

Get a full list of types of items here: http://wiki.roblox.com/index.php?title=Asset_types