Star Army allows the use of images that are licensed under Creative Commons licenses. In order to use Creative Commons Images, you MUST adhere to the requirements of the license. These requirements typically include:
Creative Commons images should only be uploaded into subfolders of the creative_commons: media namespace (Link).
Pages that use Creative Commons licensed images, or are created from share-alike images MUST state on the page that the artwork is licensed under the creative commons (including the exact license and any restrictions on use), and in a way that makes it clear that it is just that image and not the whole wiki.
In general, it's better to use a SARP-specific image if one is available instead of a Creative Commons image. They are generally used as palceholders when no SARP-owned or licensed media exists for the subject of the article.
Out of creative commons licenses, CC0 license is preferred as it is essentially public domain, followed by CC-BY.
Beware of using images that are not really creative commons. See Wikimedia's article on License Laundering for an explanation.