My pal and I got into a little debate about this, but it ended quick since I don't know too much about this topic....and I take all my own pictures and make them from scratch. But the question is - how much does a picture have to be altered before you can reuse it on your site and/or for distribution? Now I don't know if you can alter someone elses images before you can use them for you own purpose, but he was saying something like 60%. What are the laws on this (if they are any)? Or what would keep you from getting in trouble from using them?
Well, I'd say the change has to be clearly visible and non-trivial, for it to be legal. I don't think it's a percentage rule. [this is just common sense, I have no legal expertise whatsoever]
We must always respect someone's efforts and copy rights. I suggest to obtain a permission from publishers of the sites before going for any modification to the images that are grabed from other sites on internet. No one will say "No" if you use any image or something for good purpose and ready to give credit for that.
See, I was on the same page before the debate....but I guess I was swayed a little. Are there any links about this from reliable sources? Anything set in stone either?
Being a photographer, I can tell you that T0PS3O is correct. That being said, however, if you started off with someone else's image and changed it to where it could not be recognized as their's, so long as you did not admit it, then you could feasibly get away with it. But, of course, you wouldn't do something like that.
It also depends on the license under which it is published. Some pictures are GPL, some public domain, some 100% owned by the creator, some allow derivative work etc. It's a legal maze but a safe rule of thumb which will keep you out of expensive trouble is that it's not allowed.