We suggest that if you plan to submit your work to an agent or publisher, then you should consider posting in the Members' Only Workshops
. If your work is a novel, then only post excerpts rather than entire chapters.
The advice from the author’s submission service, Writer’s Relief is -
Is work considered previously published if I post it on a blog, Web site, large social-networking site, or online literary journal?
If you’ve posted your writing on any of the above sites, it is generally considered previously published.
Is my work considered previously published if I post it in a writing forum or Web board?
If the forum or Web board is private and intended for the purposes of encouraging feedback or community support, then most editors and literary agents
will consider the work unpublished. But just in case, you may want to take it down once you’ve received feedback so it doesn’t appear online.
If the forum in question is public (that is, if nonmembers can see what you’ve written), then your work will likely be considered previously published...
Generally speaking, it’s okay to publish excerpts online, as long as they are on the short side (relative to the work in question). - Writer’s Relief (http://writersrelief.com/blog/2013/11/what-is-considered-previously-published-writing/)
The situation for artworks, according to AIGSF*
Unfortunately, there is no consensus yet on whether posting a work online qualifies as a legal “publication.” The Copyright Office has refused to offer an opinion. Some people think posting online qualifies as publication because it allows multiple people in multiple locations to view the work at the same time, which is analogous to print publication. Also, in fact your computer technically makes a “copy” of the work when it displays the web page…
However, the law is clear that unauthorized copying does not count as a legal publication. Therefore, if you post your work with a copyright notice (and, for good measure, a clear statement that it may not be copied without your permission), there’s a good argument that you have not made copies of your work available to the public, and thus your posting is not a legal “publication.”
An illustration that’s been posted online for the purposes of peer review and critique doesn’t affect the marketplace for printed books. You have not given anyone a license to print the illustration in a commercial way, and there will be nothing out there in the marketplace to compete with the publisher’s book. Thus I don’t understand why publishers would consider such online postings to be a problem, especially if it is a relatively private forum, as opposed to on your website where the entire public can view it. In my practice, I have not personally encountered such an objection from a publisher. - AIGSF*
* The San Francisco chapter of AIGA, the professional association for design, is one of the largest and most active in the country, representing over 1,600 designers in graphics, interaction, experience, motion, and affiliated fields in the Greater Bay Area.