I'd say let people do what they want and we mind our own businesses, unless it's art we've done ourselves, or art done by someone we know, they're using.

My opinion. Like it or lump it.

As a journalist who is not very artistic, I tend to use clip art a LOT in my layouts. The hard and fast rule that I use is to not borrow and re-use any image that is explicitly copyrighted or not intended for other use. Everything else is fair game.

I'm a graphic designer who has to be very careful about what is used where, and here is the bottom line:

On a minuscule website such as this, the only people who really care how images are used are those who are young and very precious about what you are and are not allowed to do (I mean in general on small community sites). Essentially if you get to an image on google that has no terms of usage, then it's fair game. Chances are people who took a photo you're using as a reference for your imaginary deer on a speck of a community site won't really care about it. That doesn't mean to come across as harsh, but trust me, it's the truth.

Though I will say that I think it's very unfair for people to attack and accuse someone for theft when they themselves might have come across it quite innocently on google, this goes for all the small communities I've been a part of. You can easily tell if someone has done it by accident, or has knowingly gone out of their way to take something and claim it as theirs:
Innocent find: the image will be posted unchanged, perhaps hotlinked, and more often than not the user in question is quite young and is not aware that they might not be able to use some things they find. They will also not draw attention to it, nor claim it as theirs. It's fine to explain and ask them to remove it, but in a manner where they will not feel immediately shunned.
Deliberate: the image will be posted under a different url (private photobucket for example), and possibly edited into an avatar or manipulated in some way to adhere to the use they wish to dictate. In some cases they may try to claim it as theirs, and will be overwhelming adamant. Do not feed them!

All in all, everything I've seen on here is okay despite the few newbie discrepancies of posting random peoples artwork as avatars, but that's not a big issue at all.

Edit: Made it a bit more clear, I rambled haha.

I think if anything is copyright, signed anything in that sort of way the art should most certainly NOT be touched...

However if it isn't well I am open to using it, like if it is just a picture of a deer in a forest that had been used in a journal article or something, as a reference or other.
I do however think that the link should be supplied (for example, if you find a picture of a deer and put it up as yours put a link underneath just saying like "Original found here" or "Picture from:", depending on if you altered it or not) so that others know that that art wasn't originally yours to begin with but you are using it.

I think, unless it's stated otherwise, has a water mark, or anything of the sort-- it's fine. At any point, when you upload something on the internet, anywhere-- that risk is always possible of it being stolen, used elsewhere, innocent, or not so innocent. The idea itself. "I am going tp upload this on the internet", should be a warning itself. Be wise, and simply do not upload the picture which may be very precious to you. I have had to do this many times. Though, if a watermark is used, and you can prove the picture is yours, and it is blatantly stolen-- and used for commercial use, you have a lawsuit.