[Gello]

GetCursorInfo() says what's on the cursor. You can call that when your button receives something:

local f = CreateFrame("ItemButton","RdD",UIParent)
f:SetPoint("CENTER",-200,0)
 
local function onReceive(self)
  local cursorType, cursorID, cursorLink = GetCursorInfo()
  if cursorType=="item" then
    local _,_,_,_,icon = GetItemInfoInstant(cursorID)
    self.icon:SetTexture(icon)
    ClearCursor()
  end
end
 
f:SetScript("OnReceiveDrag",onReceive)
f:SetScript("OnClick",onReceive)