I have been weighing how to best address this issue. I have decided an example post is the best method, so here is The Steem Pope's Official Sermon on NSFW Content. And it does include an NSFW image, although it is not as explicit as most on this platform. Proceed (or not) accordingly.

What is "NSFW"?

NSFW stands for "Not Suitable/Safe For Work," and Wikipedia says it is used to refer to material that contains, "nudity, intense sexuality, profanity, violence/gore or other disturbing subject matter, which the viewer may not wish to be seen accessing in a public or formal environment including a workplace or school."

Basically, if it's the sort of thing that you wouldn't want your grandmother to catch you reading or watching, tag it.

Step 1: Use the #NSFW tag first

If posting NSFW content, using the tag should go without saying, and it should be the first tag in your post. The first tag you use is a permanent category, while others can be changed later.

Suggestion: Buffer Image

@thecryptofiend created the image above as a buffer for NSFW posts to prevent inadvertently displaying a problematic thumbnail. For a while, a glitch in the Steemit code didn't automatically hide such content if "nsfw" was not the first tag. It is still a good idea to use the buffer image in case the post is shared outside Steemit though.

Step 2: Attribution

If you are posting anything other than photographs you personally took, or art you personally created, cite your source. If you know the original photographer's website, the original page that hosted the images, or the like, link it. If it's from some third-party site, link it. If it's from something like a Tumblr or Pinterest collection, you should still link your source. If you can, try using a google reverse image search to find the source. Paste the source image URL or upload the saved image from your computer to track down the source if it's available there. Use all due diligence to be as honest as possible.

Image credit

In this case, the image credit link directs to the original source page where the image creator is identified and the image rights are stated. The markdown code looks like this:

[Image credit](https://pixabay.com/en/gran-canaria-canary-islands-1171318/)

I personally prefer to add centering tags to my credit links, but your mileage may vary. You can also use an asterisk at the beginning and end to make it italicized instead, for example, and keep the standard left justification of the rest of the text. Lastly, you could also link your image source(s) as a footnote at the end of your entire post in a list, or hyperlink the source in the body of your post. Use what works for you, but use proper attribution!

Suggestion: Hyperlink the image itself, too

Image links are similar to hyperlinks, except an exclamation point precedes the square brackets, and the URL must be a direct image link. This entire link code can be wrapped in square brackets and followed by the source page URL as in the example image above.

On its own, this is not ideal attribution, but it works. You can also repeat the image URL so clicking on the image opens the full image on its own.

This may not work with all image hosting sites, though.

Step 3: Be considerate of copyright

Intellectual property laws are a mess, but as a member of Steemit, you did agree to the terms of service which include personal liability should Steemit suffer financial harm due to copyright claims. So if there is a large photo set, post one or two images under fair use principles, and link to the page itself as part of your attribution.

Step 4: Decline payout if you do not include substantive commentary

"Check out these hot pix!" is not substantive commentary. If the images are from someone else, and you are only sharing them, it is morally incumbent upon you to decline payout for your post. Steemit is about original content, and if it's not your original content, and you are trying to profit from it, it's just sketchy behavior all around even with attribution.

Closing notes

Focus on personal virtue, not profit, even when you're posting pictures many people consider immoral content. It will pay off in the long run for your reputation, and help protect our shared Steemit ecosystem.