While most of you know we get most of our images from from AlphaCoders and its affiliate sites (WallpaperAbyss, ArtAbyss, etc...). While I personally have no problem with using images I randomly find I will always keep in mind that some might be copyrighted, but ask yourself the question; "Is this copyrighted?".
What happens if you don't know? I'll tell you, it probably is. You'll almost never find an awesome picture that's not copyrighted. But how can you be so sure and/or prove it? There's actually an easy way to do so. And that will be Google images...
Here's a quick tutorial with pictures, because that might make everything easier to follow.
Find an image you like and of which you're not sure it's copyrighted or not (but again, we all know it probably is). In this case I used the picture of a bow, a very detailed masterpiece which I could maybe use.
Step 2Open Google and go to Google Images, then drag the picture you'd like to search to Google Images. A small box should appear in the searchbar (or whatever it's called) and drop it there. Google will start searching this image on the web.
Step 3If all went correctly Google will have found many hits of the image. One of them will be the source, speaking out of experience you will have to find for DeviantArt, as most of the pictures on the web originate from there.
Step 4All that remains is to ask the artist for permission to use the image, I've asked several artists (use PM) and they were glad that I asked while others would just randomly use them without approval. Inform them of the use of the picture, provide links and be polite, but be wary that some say no. Rejection is part of life.
Also, I would like to thank 9gag (sorry for the spam) to tell me about the Google Images trick.