Alright, this was a long time coming. Herein, I'm going to give the basics on what to and not to do when it comes to uploading images!
It's a rather simple concept that, for some reason, some do not seem to be able to grasp. Having copyright means that a person has exclusive rights to something, whether it be an idea, a name, an image, a sound/song, etc. You aren't allowed to alter this image or use it in any way. When someone creates something, it becomes their intellectual property unless they choose to release it to public domain or creative commons.
Now, you may be asking: "Shelly, how do I know if something is in creative commons or public domain?"
Well, that's a good question! Good for you for asking it! :D
First, there's creative commons. Typically those that release their intellectual property into this specify how it is to be used, where it is to be used, and under what circumstances it should be used in. In other words, some rights are still reserved by the original artist. For example, there's this. I created this image as a gift for PCA, and released it into the creative commons for that purpose. However, I specified that the image could only be used on the Warriors Wiki and that I must be attributed for it. However, some artists completely release their work under creative commons "share and share alike". This means that, as long as no one copyrights it for themselves or profits off of it, it's free to use. Again, the artist may stipulate that they must be attributed for use of it.
Then there's good old public domain. It's rather simple to find an image in public domain. This image, for example, is public domain (as stated in the text next to the image). The image may be used and altered by anyone for personal or commercial purposes. And all I did was google "cat public domain image".
However, there is a very simple way to avoid any trouble with this at all.
If you didn't make something, don't upload it here or anywhere. Then you should never be accused of copyright infringement! It's as simple as that.