Font legality

I've designed the odd font over the years, one of which people seem to really like - it involved printing out an existing font, screwing up the paper, photocopying it a few times ('grunging it up') and then rescanning and redrawing it from scratch into Fontographer.

So, what are the copyright issues? Could I sell it, or is it a no-no because it was originally based on another font?

Any lawyers?