To this end,
If you want to import text that you have found elsewhere or that you have co-authored with others, you can only do so if it is available under terms that are compatible with the CC BY-SA license. You do not need to ensure or guarantee that the imported text is available under the GNU Free Documentation License, unless you are its sole author. Furthermore, please note that you cannot import information which is available only under the GFDL. In other words, you may only import text that is (a) single-licensed under terms compatible with the CC BY-SA license or (b) dual-licensed with the GFDL and another license with terms compatible with the CC BY-SA license. If you are the sole author of the material, you must license it under both CC BY-SA and GFDL.
If you want to import media (including text) that you have found elsewhere, and it does not meet the non-free content policy and guideline, you can only do so if it is public domain or available under terms that are compatible with the CC BY-SA license. If you import media under a compatible license which requires attribution, you must, in a reasonable fashion, credit the author(s). You must also in most cases verify that the material is compatibly licensed or public domain. If the original source of publication contains a copyright disclaimer or other indication that the material is free for use, a link to it on the media description page or the article's talk page may satisfy this requirement. If you obtain special permission to use a copyrighted work from the copyright holder under compatible terms, you must make a note of that fact (along with the relevant names and dates) and verify this through one of several processes. See for the procedure for asking a copyright holder to grant a usable license for their work and for the processes for verifying that license has been granted.
Context is also important; it may be acceptable to link to a reputable website's review of a particular film, even if it presents a still from the film (such uses are generally either explicitly permitted by distributors or allowed under fair use). However, linking directly to the still of the film removes the context and the site's justification for permitted use or fair use.
Contributors who repeatedly post copyrighted material despite appropriate warnings may be blocked from editing by any administrator to prevent further problems.
If a page contains material which infringes copyright, that material – and the whole page, if there is no other material present – should be removed. See for more information, and for detailed instructions.
Images, photographs, video and sound files, like written works, are subject to copyright. Someone holds the copyright unless they have explicitly been placed in the public domain. Images, video and sound files on the internet need to be licensed directly from the copyright holder or someone able to license on their behalf. In some cases, fair use guidelines may allow them to be used irrespective of any copyright claims; see for more.