When I try to add the image, the image doesnt appear but it is getting created, here is my script:
game.Players.PlayerAdded:Connect(function(plr)
local thumbType = Enum.ThumbnailType.HeadShot
local thumbSize = Enum.ThumbnailSize.Size150x150
local playerThumbnail = game.Players:GetUserThumbnailAsync(plr.UserId, thumbType, thumbSize)
local newImage = Instance.new("ImageLabel", game.StarterGui.Leaderboard.Frame)
newImage.Name = plr.Name.."Image"
newImage.Position = UDim2.new(0.5, 0, 0.5, 0)
newImage.Size = UDim2.new(0, 150, 1, 0)
newImage.AnchorPoint = Vector2.new(0.5, 0.5)
newImage.Image = playerThumbnail
end)

3 comments
also, don't use the 2nd parameter of Instance.new() as it is deprecated and slow.
OMG thank you so much! :D
Mark it as the answer then.