I posted this recently elswehere (coulda been this thread for all I can recall) but it fits here:
The pieces, when put together, reveal a picture (the specific dino picture isn't important here). In the context of evolution, if these pieces were fossils, the analogy of the way we fit the pieces together is the anatomical structures of the fossils and their ages. We end up with the well-known tree of life, showing common descent with variation.
Now it's possible that someone could come along and claim that this isn't the only possible picture we could make with those pieces, and that the picture we're showing is merely the result of imposing our prejudices on the pieces.
That might be true, but only if it were possible to arrange the pieces in some other way (for example, if the pieces were all the same shape, so that any number of mosaic designs could be produced). But that's not what we're working with. We might challenge our skeptic to try his hand at re-arranging the pieces, but no, he won't do that.
We could also point out that DNA evidence shows a close, pre-existing relationship of the pieces that we've fitted together, thus confirming the picture; and that re-arranging the pieces would be inconsistent with such evidence. But somehow, notwithstanding any other way to arrange the pieces, the skeptic will always insist that the picture is the result of prejudice.