Teaser 2996: Piece it together

From The Sunday Times, 23rd February 2020 [link]

I have some jigsaw-type pieces each consisting of one, two, three or four 1cm-by-1cm squares joined together without overlapping. The pieces are black on one side and white on the other, and they are all different. I have used all my pieces to simultaneously make some different-sized white squares in jigsaw fashion, with each square using more than one piece. Even if you knew what all my pieces were like, you would not be able to determine the sizes of my squares.

How many pieces do I have?

[teaser2996]