I'm building a library from methods that I've found on the internet. Some are free to use or modify with no requirements, others say that if I leave a comment in the code it's okay to use, others say when I use the code I have to attribute the use of someone's code in my application (in the credits for my app I guess).

What I've been doing is reorganizing classes, renaming methods, adding descriptions (code comments), renaming the parameters and names inside the methods to something meaningful, optimizing loops if applicable, changing return types, adding try/catch/throw blocks, adding parameter checks and cleaning up resources in the methods.

For example;

I didn't come up with the algorithm for blurring a Bitmap but I've taken the basic example of iterating through the pixels and turned it into a decent library method (applying the aforementioned modifications). I understand how to go about building it now myself but I didn't actually hit the keystrokes to make it and I couldn't have come up with it before learning from their example.

What about code people get in answers on Stackoverflow or examples from Codeproject? At what point can I drop their requirements because at n% their code became mine?

FWIW I intend on using the libraries to create products that I will sell.