To be honest I don't know about changing the hue on a photo. I don't know that much about it, but enough to try and stay out of trouble. Like I said some people don't mind and others do. You just never know, but using photos without a copyright, name or watermark on it might be the best thing to do. But don't hold me to that, it wouldn't be the first time I was wrong.
As I stated for the most part I don't think people mind and long as your not making a profit from it. But you never know some people will sue because they didn't give anyone the rights to use it. I would use Creative Commons photos to be on the safe side. But it's up to each person what they use and how they use it.
All I can say is, I own the copyrights on my paintings and photos of my paintings. I could sue someone if they use my photo. Will I? If I find out they are making money by using my photos, you bet I'll sue them. Unless they are smart enough to ask and let me know what their doing with it and why. Who knows I could say give me $50, $20, $5 or say, sure go ahead and use it. It's amazing what you can get by asking someone sometimes.
The 75% is what the copyright owner stated. He is in a different country so I don't know the laws. It would be like me saying you have to change my painting by 75% before you call it your own. I have a hard enough time trying to keep up with US laws. As you know one day it's okay the next day it isn't, or it wasn't but now it is. I can do it, But you can't. You know how it is

This might be an example. I use to do voice overs and I did some for free to help out hobby broadcasters. I own the rights to my voice, right? I offered to do free voice overs for hobby broadcasters. You know what happened, I ended up doing free voice overs for Sky News in the UK and the largest radio network in India. Now these are two big time radio networks they should have paid for them. Could I sue them yes but seeing they are in different countries makes it more trouble than it's worth. The funny thing about the Sky News one is, I was on Skype with a couple of DJ's from the UK and I was playing demos. I played one and one guy says, HEY! I hear that all the time on the radio over here, That's you? That's how I found out Sky News was using my voice.
Sorry I kind of went on a rant... Get me going on copyrights etc. and sometimes I don't know when to stop LOL
Anyway I bet you have more questions than answers now
