I usually look and analyze websites/effect from websites that seams interesting to me. So I found a website that was bought from templatemonster. That website uses an effect on an image, a hover transition. Analyzing that code I saw an file named "hoverSprite.js". http://pastebin.com/dbxm7zYT . I tried to find that code on the net and no results.. My question is: can i use that piece of code on my commercial projects ?
I am not a lawyer so do not take what I'm saying as legal advice. It is merely my personal opinion and may be wrong.
The law probably varies from country to country.
Generally, though, it's not legal to just outright copy large pieces of people's code. If you find a license notification indicating that it is licensed permissively (BSD license, MIT license, Apache license, etc.), then you can use it (assuming the person who put the license there did so legitimately).
Otherwise, you can ask the site administrator where they got it and/or if you can use it.
You can also study the code and learn from it, then implement your own code specific to your site. (Do not just start modifying the existing code. Write your own, from scratch.) Again, the law probably varies from country to country, but that practice will generally not get you into trouble. (Truth be told, just copying the code will generally not get you into trouble even though it's not legal; you shouldn't do it anyway.)