How to tell a Scratch from a Crack in a Cylinder?

I say it's a scratch too.

You could have the block magnafluxed.

Might be cheap enough at a machine shop, I assume the block is empty at this point.

If it were a crack it would have some signs on the surface that is 90 degrees to it (top in the photo)

Plus cracks are not that clean they follow the grain of the metal.

Plus the second mark to the left (in the closeup photo)

If it really bothers you you could bore the cylinders but then your budget would increase by a few thousand dollars for oversized pistons, and machine work.