There are freely licensed media resources (also public domain) that can be used as sources for file upload at Wikimedia Commons. However never blindly upload everything from these pages. Please always double check if the media is really freely licensed and if it is useful for Wikimedia Commons projects. Thus it is required to act according to the following points.
Before you upload in the Commons any media from these sources:
Check if it is already available in the Wikimedia Commons - See the search page.
Never forget to include a good description, credit to the author, source and the right license tag (and justify, e.g. with a quote, why this license tag is right) - See project scope.
Please don't data-dump
Not all resources are useful for Wikimedia projects. Examples of non-useful resources include: images without informational value (party pictures, minor artwork without informational purpose), very old media which may have errors of fact, content from biased points of view. See project scope.
Before you add a source link
Check if the website with the link has a fair amount of free licenced content with a useable licence.
Free content search engines and indexes of mainly Creative Commons licensed material. Be aware that not acceptable non-free Creative Commons licenses are included in the search engines as well.
Please also take a look at the bad sources that are not acceptable for Wikimedia Commons in order to avoid common mistakes.
