Citing sources in posts is important for a number of reasons, and not just because if you fail to do so you may get a comment from ourselves. Why do we, as Steemit users, need to cite our sources? To produce and share quality posts with original content. Plagiarised and copy/pasted material, including images, is not original content. Plagiarism is often a violation of Intellectual Property, which is generally seen as the theft of intangible property.
We get that some people may not understand what plagiarism and Intellectual Property are. Our goal as the 
Plagiarism
Plagiarism refers to the act of obtaining a piece of another person’s work and presenting it as your own. Taking the ideas of another individual, copy and pasting entire sentences, rewriting a paragraph in your own words, translating something from another language, and copying parts of posts from other users are all examples of plagiarism.
There are numerous tools, the main being Google search, out there that make discovery of plagiarised work rather a simple matter. Even if a paragraph has been translated from another language and slightly modified, detecting that it was obtained from a different source than yourself is easy. Think of it this way; if you were able to find this content and repurpose it, others can find it as well.
Plagiarism can be avoided through careful referencing of material. Adding sources to everything that did not originate from your own head is vital to your content being original and protects yourself and your account from accusations, flags and legal action.
There is no downside to citing sources. Citing sources provides the necessary referencing and allows your readers to further explore the topic through external sources. Most importantly, it gives credit to the original creator or author of the material. The more you cite the better quality your post becomes.
Intellectual Property
Intellectual Property refers to artist works, writing, inventions, documented ideas and a whole lot of logical assets. Intellectual Property Rights are a very serious matter and issue surrounding their misuse, both deliberate and accidental, have resulted in law suits and criminal charges.
A photograph taken by a professional photographer and shared on a wallpaper site, for example, is subject to a specific license agreement. The photograph itself is the intellectual property of the photographer. While users may download the photograph to use as a wallpaper on their own home computers, the license agreement may explicitly prohibit the use of the photograph anywhere where commercial rewards may be obtained. This includes on sites like Steemit where users receive monetary compensation for posting content.
It is vital to check the licensing of a particular piece of intellectual property before sharing it in a post, even if the post links back to the original source. Failing to do so may get you in serious trouble in the long run, particularly as posts older than 7 days can no longer be edited to remove offending content.
Typically, when the rights relating to do with a piece of intellectual property are breached, the offending party receives a Cease and Desist notice. This is the mildest form of legal intervention and basically means that remedial action must be taken upon receipt of the letter. However, once the 7 days pass, the STEEM blockchain no longer allows for removal or editing of posts. Thus, posts cannot be removed and users cannot comply with the notice. That may lead the intellectual property owner to escalate the situation and initiate a law suit.
The best way to deal with such situations is to avoid them entirely. For this reason, ensuring that you carefully select and document every piece of external information, content, or artistic work in your posts is vital.
Citation
It is not sufficient to simply note that “text source is Wikipedia”. A link to the specific Wikipedia page where the content came from is required. If numerous sources were used, adding the source after each separate idea is recommended.
Every copy/pasted sentence should be either in quotes “” or formatted using the > markup.
Every paraphrased paragraph, sentence or idea should have a reference as close to it as reasonably possible to indicate its origin.
Example of Citation
Apples are a true superfood in my opinion. "Researchers have long been aware of the potential for apple consumption to support balanced populations of bacteria in our lower digestive tract." Source The antioxidant contained in apples is referred to as Quercetin and researchers believe that it prevents damage to human brain cells. Source
The above example post has one original sentence:
Apples are a true superfood in my opinion.
The next sentence is copy/pasted from its source without alteration and is thus in quotation marks:
"Researchers have long been aware of the potential for apple consumption to support balanced populations of bacteria in our lower digestive tract." Source
The last sentences is paraphrased information from a different source:
The antioxidant contained in apples is referred to as Quercetin and researchers believe that it prevents damage to human brain cells. Source
If you look at the linked sources, you can see where the information came from and how it was originally presented. A post that cites sources in this manner adds a lot of value to your blog and to the reader. It allows your reader to learn more by clicking on the sources and it makes your blog look professional. It also prevents you from being accused of plagiarism.
Images
Sourcing and citing images and media content is a trickier matter. First, you must ensure that you may reproduce the image or piece of media in the first place.
Pixabay and Creative Commons CC0 Images
One popular source for "free images" is Pixabay. To ascertain how these images may be used, one must refer to the Terms of Service posted on the Pixabay website. According to the terms, you may not use bots to automatically collect the images or use a very large amount of them (aka mirror the image database). What you can do is subject to the Creative Commons CC0 agreement.
You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission. Source
What Pixabay did is roughly summarise the CC0 parameters for you in the statement above. Remember, just because the image is offered under the CC0 license, it does not mean there are no ramifications for its misuse. More information about misuse can be found here. Remember that your posts receive monetary rewards. Taking the same sort of precautions that a business would and ensuring you're fully versed in the licensing is recommended.
Photography from Google Searches
Typically, when someone needs an image for their post their first stop is Google Image Search. You can find some good stuff there. The problem is that Google and other search engines archive crawlable content irrespective of licensing or ownership. For this reason, it is vital to ensure you are explicitly permitted to use an image.
Taking photographs and repurposing them for #colorchallenge or #photography contests without a) verifying if you may use them and b) giving the photographer/artist credit can have severe implications.
One service that photographers use is called Pixsy. The service scours the web for unauthorized use of proprietary images and leverages escalating legal action against violators. They don't care that you included a link back to wherever you found the photograph; their priority is ensuring the photographer retains control and distribution of their Intellectual Property.
For general images, such as stock photos that you found on a news site for example, a link back to the source suffices. Make sure that you link back to the website on which the image appears, not to the image address. A user should be able to click on a link and see the image as it was originally intended. If no website exists (if the image is in a directory or part of a Facebook album) then find a different image.
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