Wikimedia Commons:

Lord knows, Wikimedia Commons is not new. It’s Wikipedia’s baby
sister, just as useful, just as smart, twice as pretty, but for some
reason not as popular. Go figure. Puzzles me to no end. Thus you find
me writing a post about it just because I am constantly astounded by
how many people don’t know about it yet. Alright, so here is what it
is good for.

I can’t begin to count how many times people have asked me for tips on
finding images that are legally safe for them to use in their
presentations or papers. Or that I’ve seen images in presentations and
known for a fact that the images were not legal to use, or were not
properly attributed or cited. Basically, if you want to use someone
else’s images, pics, graphics, graphics or photos that you did not
take yourself or make yourself, there are certain things you have to

1. Get permission
2. Include info about the image: what it is, where you found it, who
made it, etc.

Getting permission is often complicated, UNLESS the image is really
really old (out of copyright) or the person who made it already gave
permission to the public. I’m not going to going to go into the
subtleties of this, in part because Wikimedia Commons makes it so much
easier. Basically, every image in Wikimedia Commons includes all the
information you need to use it, including the original source, what is
legal or not, and how to cite it so the creator is happy and you don’t
get in trouble with the law. Click on any image or video clip or other
media, and scroll to the bottom of the page. That is where all the
licensing information can be found. Just do what it says!

Please note that this is very different from most other Creative
Commons or "Free Images" search engines, which often do not verify
that the image really is free. Even if you do your best to only use
free images, you can still get in trouble if someone else stole the
image and then marked it free. There is no easy way to find out. That
is why I so like using Wikimedia Commons, since they list the
provenance of the image. So responsible, and so nice to have a place
for media that is so much more trustworthy than most other sources.