CC0 - Public Domain Free to use anywhere where you want and no other requirements.

CC-BY - Free to use but original author must be attributed. Usually there are instructions how to attribute. Creative commons also forbids art to be DRM protected so CC-BY is problematic with iOS apps.

OGA-BY - Same as above expect DRM clause has been removed.

CC-BY-SA - Free to use but original author must be attributed and if art is being modified this new art must be redistributed with same license. This might be a bit problematic license since there a big debate if this binary code is consirider as a new art. Screenshots and videos taken from game using CC-BY-SA are mostly under this license. Also CC-BY-SA has DRM clause which makes it problematic in iOS apps.

Here at OGA here is thread about CC-BY-SA:

http://opengameart.org/forumtopic/practicality-of-cc-by-sa?page=1

Also Creative Common has published human readable forms of their license:

https://creativecommons.org/publicdomain/zero/1.0/

https://creativecommons.org/licenses/by/3.0/

https://creativecommons.org/licenses/by-sa/3.0/

I haven't used GPL licenses as for art so I cannot say about them...

Since I am not lawyer you should read the license text also and try to understand them...

Licensing can be complicated. Previous poster did a good job of explaining the usual Creative Commons licenses for artwork. I specialize in knowing software licenses.

The GNU General Public License (GPL) is a copyleft license, which means that it works like the CC-*-SA licenses. You must release derivative works under the same license (or in the case of GPLv3, you may also release it under the AGPLv3, discussed below). The GPL says that all who receive a licensed copy of the work have the freedom to use the program as desired, change the program as they wish (source code is required for this), distribute verbatim copies of the work, and distribute copies of their modified versions. These are the basics of free software, the idea that computer users should be free to do their computing as they wish, not as some other entity wishes. Free software has nothing to do with price. Keep than in mind if you ever see that term. Also, do not confuse free software and freeware. Freeware is nonfree (proprietary) software that you can get at no cost (gratis, as we say).

The GNU Affero General Public License (AGPL) is also a copyleft license. Version 3 is identical to the GPLv3 in every way, except with one additional clause: if the software is interacted with over a computer network, that interface must expose the corresponding source to the software in use, so that all users could modify it and put up their own version if they so desired. This is the license I use on all of my original software.

The Expat license (commonly called the MIT license or X11 license) is a permissive license. Essentially, it says you are allowed to do whatever you want except claim warranty from the copyright holder. I do not recommend this license, only because it uses some unclear language such as "significant portions" of the software, which has no legal definition.

The ISC license is a permissive license identical to the Expat license, but with clearer language. If you want to use a permissive license, I recommend this one.

There are many more free software licenses. You can read about all the notable ones here: https://www.gnu.org/licenses/license-list.html

If you have any questions, just let me know. Happy hacking.